First, we need to determine what about FeralHeart is causing this die off, and fix it. I honestly don't think the graphics are even part of the problem. Some people like good graphics, sure. But as an art style there is something appealing and relaxing about the way FH is.
I can think of a few things:
1) Distribution: Right now, if something isn't on Steam, or a similar service, a game generally isn't going to be found in the first place. We should really try to get something like this released on steam, and if possible try and subtly influence a few influential YouTubers to promote it on their channels.
2) Gameplay options: You had already mentioned fixing this with a survival mode, which would be great. However, that niche is already pretty well covered by the now-revived WolfQuest. However, it is intended as an educational game, and I think if you had a sortof blend between this and something like Tokyo Jungle, you would be in good shape. You would just have to make it 18+.
3) Dev team. Kovu leaving the project really did this game in. So much could have been fixed up if the team had access to the source code. If you want to make it yourself, go ahead. If you want a team, that can speed things up, but be careful to not have a team member leave and leave the rest of the team helpless. Just share all the necessary information ahead of time, so if someone does leave you can replace them.
4) Find your niche. Wolf survival is already pretty well covered by the restart of WolfQuest. Shelter is already popular on Steam. Find something that makes your game stand out.