Once you reincarnate skills should return to previous highest level (never passing the level max, of course, we don't need superb bashing level 3's) without having to go to a guild. If you superb a skill it should return to superb without additional practice once you hit the level where superb is available. No one wants to have to stand naked in Solace square for 4 hours training hide more than once per wipe.
Now that I say that, I can think of several players that would gladly stand around naked...and they don't even play thieves!