Take the high road. I know a couple of bassists who are fantastically talented players, yet I never see them out gigging b/c of smart-arse stunts they pulled 10 yrs ago. Let's not forget that some of these guys happen to be your friends. Obviously when they were concerned that you might not be able to pull double duty, they should have come and talk to you, but you get the opportunity to be the classy guy here.
If you don't have time and/or don't want to show their new bassists how to play, just decline nicely. They've already made it awful clear they can't pay for you to fix the error of their bravado (as in replacing you with a guy who owns a bass he doesn't know how to play). Revenge is great, but it will be so much better when 6 months from now they approach you to ask you back while fully knowing they effed up and you were totally cool about it.
Plus, it sounds like you are in a better band now, thats were your energy will be best spent.
Good luck!
If you don't have time and/or don't want to show their new bassists how to play, just decline nicely. They've already made it awful clear they can't pay for you to fix the error of their bravado (as in replacing you with a guy who owns a bass he doesn't know how to play). Revenge is great, but it will be so much better when 6 months from now they approach you to ask you back while fully knowing they effed up and you were totally cool about it.
Plus, it sounds like you are in a better band now, thats were your energy will be best spent.
Good luck!