If gameplay itself is dependant on online servers, the game has to release a working version of the server code so it at least could be run by fans, or be refunded.

I replied to one of it a while ago and basically, this part is impossible since developer also “license” 3rd party backend/plugins/software solutions to make their server working. The developer do not have the right to release licensed code/api etc.

meaning, say if a backend have the free learning version of license, the developer are bound to the commercial license, which dictates if they can release code that involve 3rd party code/api.