Old characters should be there, you can log into your plaync account and see if your account is still there(should be).
I played a few years ago, resubbed for a month or two again, maybe 3-4 months ago, was still decent, should be at least a few big new things for you to do if you've not logged in for years. New power options for most classes, then the villians part of the game aswell if you fancied buying that and trying it also. A lot of people prefer Villians as things like the mastermind class is pretty damn awesome.
No harm in resubbing for a month though, infact as you get a month free with the game, buying the villians version might be the way to go.