A token that’s created as a copy of another object will remain a copy of that object after it leaves the battlefield. Assuming it copied something with a mana cost, the token will still have that mana cost, so it can be cast as normal from wherever it is if you have permission to do so. Note that this is different than a token that becomes a copy of another object and then leaves the battlefield. In that case, the copy effect wears off as the token leaves the battlefield.