Where to go from here? Well I would stop speculating on whether or he comes back or not. All signs point to no and it seems he's all but ghosted other people who have worked on the game closely with him. All open source masters are on github and others working on it and abandoning it. With all due respect, He should always get a credit of some sort, but the game needs a full overhaul and someone else behind it. Period. If people keep picking up the code and tinkering with it once every 3 months; just biding their time, thinking maybe... *just maybe* Vin will return and explain his left-handed coding on the game, then the game will continue to stay in this state.
The 'maybe' and the 'if' is the key in your dialog.
I'm one of the many who spend the time on the sourcecode and abandon it after 4 months of studying. (My facelifted sourcecode version can be found on the discord's modding chat, because I share that, hoping to someone can step further with it and saves a lot of time for herself)
So I wrote a short list of my consequences:
1. Vin did the coding of the game but get animations and other staff through his loverslab contacts (see the faq file under the modules folder) so it is not a one man band's game, and I didn't think he get this materials for free
2. overhaul the appearance of the game needs investments. There isn't usable free erotic contents (animations, models, props, clothings, etc) in the market so it's require a financial investment (without them what to add/replace/upgrade?)
3. the game engine is outdated, from this cannot use better models and newer technologies (visuals will suffer, content remains the same)
4. the builtin streetmap plugin is outdated, this means with a newer engine must be upgraded, and requires to be generate new maps because old ones are incompatible (around 190 premade map exist to the game)
5. with using the UE5 code must be to clean up (it's really messy) and repair, because key elements aren't working as intended (like the charactergeneration) and requires at least a very good coder with experience and knowledge in ue5
6. the ue4 engine will lose the support soon, so cannot be maintained too long, not with planning upgrades, or put something new to the game
7. existing animations isn't support some technologies like physic simulation, so no bouncing tits floating hairs or clotches with them on the future, and should be remade/replacing (to be clear requires animator knowledge)
8. this business model with commissions and periodic forced updates cannot be maintained too long in the future, the game is full of different content, imo unnecesary to add more without sense (and say nothing about they quality)
9. some programming concept reached they limits, must be rethink and if necessary remade
10. missing responses (or any form of communication) from the developer (knowledge of code pieces and their function and destination)
Etc..
So your "full overhaul and someone else behind it" theory are should consist from at least determination, knowledge, time, money and staff. It seems there isn't much applicant for this task, and I fully understand why. Anyone who tried bumped into at least one unbreakable/unresolvable limitation, and drop the project when something runs out from above. Someone said earlier is better worth remade from scratch, but this is only partly true.
So complaining this state of the game is understandable, but senseless (sry, no offend).
It would have been better if the dev finish and close it, but he abandoned it (no matter the reason why) leaving a mess. But it's a similar fiction with the 'if'. All respect to the dev but he is the one who decided the fate of his creation, all signs indicate that he doesn't want to deal with it anymore, and this is the fact atm.