JetBrains which creates IntelliJ etc is nice this way, they give you a permanent license to the last version released while you were still a customer (provided you are a customer for more than x months first.)

I find this both smart and nice: you can pay monthly and still get a permanent license so you won't be trapped.

Full disclosure: I use Netbeans which is free from the start and which I like better anyway, I'm just saying Jetbrains seems to be a nice company ;-)