I think the most realistic alternative is to just have an ‘earliest end-of-life date’ plainly visible at the time of purchase. Keeping these games online forever isn’t feasible, but shutting down something people paid for with the expectation of continuous service isn’t good either. Just make it clear how long the developers WILL support the game for, at the very minimum, and let people make their decision based on that. And mandate refunds for any live service game that doesn’t last as long as promised.