Warning: Potential spoilers but I am pretty sure I generally avoided them.

When one completes the game siding with the Railroad but also progressed the Brotherhood faction quest to the furthest possible point to still allow the Railroad ending, Paladin Danse may become unresponsive in the end game only offering to trade items and refusing to otherwise talk or be recruited as a companion. This small fix should allow him to respond again and break out of his literally catatonic state.

Alternative using console commands:
I just recently considered this after messing with quests a bit more, but these console commands (thus PC only) should achieve the same effective result as this mod. If the mod fails to work for you, or you would rather a quick and easy fix, try these (be sure to make a separate/backup save first). Open the console (tilde key on PC) and enter these two commands:

• 5de4d.SetValue FollowerEndgameForceGreetOn 0
• 5de4d.AddToFaction a1b85 1
  

These commands basically 1. prevent Danse (RefID 5de4d) from discussing the ending by unsetting his force greet variable (FollowerEndgameForceGreetOn) that makes him not follow you properly and 2. Adds him to the HasBeenCompanionFaction (a1b85) so he can be recruited again. I have tested on the same save I tested my mod and it seems to work just as well (I did have to walk away and approach him again a couple times however before he responded). As stated below, this only is intended after his companion quest is completed and in the endgame.


This actual issue appears to be caused by the companion recruit scene having its start greeting only occur in the post game if Danse was previously the players companion, as a fix I simply removed that condition. This flag may have been cleared when the player becomes enemies with the Brotherhood.

There is also a post end game conversation with Danse that only occurs if you won the game only with the Brotherhood and/or Minutemen. If this dialog isn't completed Danse, while able to be your companion from the above fix, will not follow you properly. To fix this I allowed this conversation to progress for the other endings as well. The choices presented are the same as a Minutemen ending, one dialog from Danse is skipped as it directly references the Brotherhood or Minuteman, and there is no appropriate Railroad or Institute topic, but it doesn't really affect the overall dialog. There is also one choice (2nd dialog choice, question response, "peace?") that causes Danse to say something that makes absolutely no sense in the Railroad/Institute ending, so you will have to forgive that lore break, or maybe spin it as Danse being dense or very sarcastic.

This fix should generally only be used for a play through if you specifically run into this bug in the post-end game, I can't speak for any effects it may have on normal game play pre-ending or post-ending without this issue. Since others reported my additional combined railroad/institute fix also worked and I saw no adverse effects using in place of the the railroad only fix, I will make the combined version the main file. It should now work for all factions (BoS and Minutemen were already there) as they are all represented in the appropriate dialogs.

Additionally, once you clear the end game dialog with him and recruit him as a companion at least once (even if you dismissed him), then continue with a save which fulfilled those conditions, you can safely remove this mod and he should respond normally. However any affected save before that will still be broken without the mod, and the above pre-ending warning applies so you should remove the mod if/when you start a new character.

This mod was made using the beta release of the official Creation Kit.

Patch Reproduction Steps (Railroad and Institute):
1. Locate Quest: COMDanse->Scenes->COMDansePickUpScene->Start Phase->Start Greeting->Conditions
2. Delete [GetInFaction Faction:"HasBeenCompanionFaction" == 1.00]
3. OK (close Topic Info window)

4. Locate Quest: (COMDanse->Scenes->)COMDanse_13_PostMQ302->Start Phase->Start Greeting->Conditions
5. Duplicate [GetGlobalValue Global: 'MQWonMin'== 1]
6. Edit duplicate's parameter to [GetGlobalValue Global: 'MQWonRR' == 1]
7. Again Duplicate [GetGlobalValue Global: 'MQWonMin'== 1]
8. Edit second duplicate's parameter to [GetGlobalValue Global: 'MQWonInst' == 1]
9. OK (close Topic Info window)

10. Locate Quest: (COMDanse->Scenes->)COMDanse_13_PostMQ302->Phase 1: Loop01->Nuetral/Blue Response #2 ("I don't know what to say.")->Conditions
11. Edit [GetGlobalValue Global: 'MQWonMin'== 1] to be an OR condition
12. Duplicate the modified [GetGlobalValue Global: 'MQWonMin'== 1]
13. Edit duplicate's parameter to [GetGlobalValue Global: 'MQWonRR' == 1]
14. Again Duplicate the modified [GetGlobalValue Global: 'MQWonMin'== 1]
15. Edit second duplicate's parameter to [GetGlobalValue Global: 'MQWonInst' == 1]
16. OK (close Topic Info window)
17. OK (close Quest: COMDanse window)

Feel free to use these steps in any other mod/fix/patch or if you want to modify/improve upon it.

This mod may conflict with other mods that alter Paladin Danse, specifically his related quests. As well, it could break him and his related quests if used before the appropriate end game state.