Sure they will... I bet some will just move to whatever game is due to be released next week.You seriously think that most of his patrons are going to run to the next incest lover who they don't know and don't know if tomorrow he's going to have a big exam and cancel the whole project, leaving them with nothing and running with their money?
No you can't be involved in the patches yourself...But you CAN make the game patchable so some other person (perhaps someone you know) can patch it back to the original incest theme.DMD was thinking in similar way. I do believe that semi official patches will be banned as well. And Patreon will start to ban games after couple of reports.
In fact why not talk to one of the modders here who have added and changed huge sections of story to your game for some help on this front?
I'm sure they could easily make a mod that turns this game into a non-incest story (perhaps a boarding house) so you could continue to at least finish off the the few scenes needed to make a proper ending, that could just as easily be modded back to the game you currently have. As long as you yourself don't release the Mod there is little Patreon can do about that.