Fair enough, but that's a huge imposition on everyone for what probably comes from a very specific instance in your life of a single game that you loved having its server die after a while, long after you got your money's worth.
Nobody is even asking you to maintain the code.
You had it working when I purchased the product that required the code.
Just share that code. I'll even fiddle around with hard-coded paths or whatever you think is making this impossible
If you really don't want to bother with that - don't sell the game, sell timed access and shut it down once the last subscription runs out.