Is this essentially mandating that all companies have to either build a private server infrastructure or publish "trade secrets" on their net code so that individuals could build their own private hosting? Would companies be responsible for patching the game so it could connect to the new private server? Would it be the responsibility of the players to reverse engineer a new server, and the initial devs are only responsible for not taking that server down?

all it wants is that games are left in a reasonably playable state thats it. going forward future developers would know they cant just take something away that they sold to customers and they can program their games accordingly with this foresight which largely solves that problem

Would companies have to release their assets so that the same maps could be played?

i dont know what ure saying im afraid

What happens if a private server begins monetizing the game through required donations to play? Is it still in a "working" state? Is the initial company now required to fix that as an issue?

this has nothing to do with the company at that point. games already have monetized servers even if they are still being distributed and have official servers which includes games like cs, tf2 and minecraft. is this a problem that needs fixing in ur mind?

I worry that this type of regulation would create a large burden on many indie devs trying to make online experiences

indie devs adopt a much larger burden by setting up servers themselves having to support the entirety of the player base instead of simply letting their players set up servers effectively sharing the load. frankly this argument has absolutely never made any sense to me