What does the mod do

In short:
All actions in combat - attacks, dodges and rolls, parries and counterattacks - spend stamina.
 
Details:
1. Combat changes.
The base stamina regeneration in combat increased to 25/s from 10/s. Base values of stamina cost and stamina regeneration delay after an action has been changed according to the list:

• Light attack. Cost is 10 stamina, delay is 1.0 second.
• Heavy attack. Cost is 15, delay is 1.5.
• Dodge. Cost is 8, delay is 0.8.
• Roll. Cost is 18, delay is 1.6.
• Parry. Cost is 5, delay is 0.5.
• Counterattack. Cost is 10, delay is 1.2.
  

Parry is calculated for each blocked hit. A successful parry or counterattack may require more stamina than the base value. Stamina cost will increase by 2 times in case of heavy enemy attack. A second multiplier will also be applied depending on the type of enemy: *1.05 for animals, *1.25 for monsters, *1.4 for vampires. For example, it takes 25 stamina to block a monster's heavy attack.
With low stamina, obviously, the action will not be performed. Also in this case there will be a warning sound effect that already exists in the game. However, this does not apply to unsuccessful counterattack and parry. In both of these cases, there will be no sound effect (it will be indistinguishable due to the blocking sound). If there is not enough stamina to parry, an additional stamina regeneration delay (from 1.5 s to 2.5 s) and a stagger effect will be added. In addition, the block will not work - the attack will deal damage. There are no additional penalties for a failed counterattack. Stamina does not decrease on failed actions.
Stamina cost while sprinting in combat reduced from 12.5 to 6/s.
2. Sings changes.
To be able to use signs directly in combat, and not run away, in order to restore stamina for this, the stamina cost for signs have been decreased. Regeneration delay has been increased for balance. Basic sings cost 50 stamina instead of 100 and have a 1 second delay (instaed of 0.5 s). Cost and delay for the alternate signs changed by about 1.5 times:

• Aard. 40 stamina cost / ~0.5 s delay. Was 60 / 0.3.
• Igni. Initial 35 stamina per s / 1.5 s. Was 50 / 1.
• Yrden. 25 per s / ~0.5 s delay. Was 35 / 0.3.
• Quen. Initial 10 stamina per s. Was 15.
• Axii. ~15 per s. Was 22.
  

3. Skills changes.
Added additional passive bonuses to skills of different skill trees. Relevant lines added to skill descriptions. Blue skills increase stamina regeneration during guard by 0.5/s per level. Red and green skills reduce stamina costs and regeneration delay by 1% per level respectively. If a mod is used that increases the number of skill slots, the reduction value from red/green skills will be reduced linearly down to 0.2% per level. For example, for 28 slots it will be 0.8%. Checked on Slots Slots SLOTS  from Zur13.
4. Decoction property changes.
In order not to break the balance, changes have been made to the properties of the following decoctions:

• Archgriffin decoction. Instead of spending all the available stamina, half will be spent. The description of the decoction has been changed accordingly.
• Ekhidna decoction. Vitality regeneration coefficient reduced from 0.1 to 0.02. Such a significant reduction does not make the decoction useless, as it restores % of vitality on any action that reduces stamina.
• Ancient Leshen decoction. The maximum possible summation of the effect is set to 15 times. In other words, the maximum additional value of stamina regeneration is 30/s.
• Werewolf decoction. Reduced efficiency. The maximum increase in energy regeneration is 30/s instead of 50/s.
  

Notes:
1. The dependence of the stamina costs for parry/counterattack on the type of enemy does not mean that the mod allows you to block and counterattack any attacks. You won't be able to parry an attack that wasn't blockable in the vanilla game.
2. If the counterattack didn't happen (not necessarily because of low stamina), most likely, there will be a parry attempt instead. Keep this in mind in combat, as you may miss a hit due to trying to counterattack with low stamina.
3. Keep an eye on your remaining stamina, use alchemy and appropriate equipment!

Additional features

1. Additional info have been added to the character stats menu in stamina section (see images of mod). Displays the current regeneration value during guard, the maximum possible regeneration value in combat/during guard (details below) and the total reduction in stamina cost/delay for combat actions.
2. If you don't like the current low stamina warning sound, found "function CombatStaminaWarning()" in r4Player.ws script and change the line "SoundEvent("gui_ingame_low_stamina_warning");" to "//SoundEvent("gui_ingame_low_stamina_warning");" and the line "//SoundEvent("gui_no_stamina");" to "SoundEvent("gui_no_stamina");". This will change the sound. However, keep in mind that this sound event is quiet enough that you may not hear it during combat.
3. Integrated change of the stamina regeneration bonus depending on the type of armor. The current values of stamina regeneration in combat and during guard depend on Adrenaline Points. The calculation system is described in detail on the mod page.
Although the principle is the same, exact values have been changed. "Steps" of regeneration value are in increments of 0.5 AP, reaching the maximum values at 3 AP. In addition, the regeneration bonus is now non-linearly dependent on adrenaline - the first AP will give a 60% of bonus, the second - 30% and the third - 10% (a fractional AP will give half the corresponding percentage). This decision should give value to adrenaline, but not make the fight too dependent on it.
If you want to disable stamina regeneration dependency on adrenaline, found "public function CombatStaminaArmorRegenChange()" in playerWitcher.ws and change the line "return true;" to "return false;". Then two additional lines in the character stats menu will also be removed. However, the value of the armor regeneration bonus will remain reduced by 40% of the vanilla value, so as not to break the balance of the mod.
4. Integrated modIncreasedStaminaRegenFix. This is an additional mod that is intended to remove the increase in all types of stamina regeneration when increasing the total stamina. You can find this mod separately on the Yellow Mutagens files page.
In update 0.2 of current mod, the ability to increase the total amount of stamina has been removed. However, it was decided not to remove increased regen fix. In general, the ability to increase total stamina complements this mod well, so I recommend using Yellow Mutagens from glassfish777, or some other mod with similar mechanics.
5. The stamina cost and regeneration delay for attacks while playing as Сiri have been removed. The mod does not change Сiri gameplay in any way.
6. Adding a missing gap to the Yrden/Axii duration stats has been moved to Brothers in Arms.

Install and uninstall

Nothing special. Unpack "modStaminaBasedCombat" into /mods folder. Don't forget to use Script Merger if necessary.
You can delete mod at any time, it does not affect saves.

File information and other

The 0.2a version runs on game version 4.04. The next update may contain some balance changes.
Mod edits files listed below.

Special thanks

Thanks to Zeebabs for his mod, which initiated the creation of this alternative version, and permission to use some ideas.
Thanks to MerseyRockoff for his advices and BiA authors for big work to fix game bugs.