If the forums goes to a completely different software there's a good chance that some features will disappear if they are not compatible with the new one. Posts will stay though.
I do know that one forum did upgrade versions and we had to redo (i.e. request) the friends list again (it was no big deal to me but can be a pain). I can't remember what else changed- it's been a few years. Can't comment to the like feature as we didn't have that there- actually we do- it's just called "THANKS" rather than "LIKE".