I feel at a certain point, if you've sold software that calls home and you are unwilling to maintain the servers and there are still people using it, you should hand it off to the Internet Archive or a similar org so they can run it. Leaving users stranded with no hope of using software they're familiar with, have paid for, and have supported is just a bad move.
Moves like what Autocad did to you are why large companies are using libre software, if upstream dies for some reason, your business won't click off tomorrow.