In the Game Room, there’s a thread about craps, it originally ressurected a 11 year old zombie. To his credit, Marley split if off, making the ressurecting post an OP to a new thread. 2 questions:
1.Why isn’t this done as a matter of course?
2.Was the original thread locked?
(mor interested in #1)
If the resurrected thread is a reasonable continuation of the previous discussion, then that’s where the discussion should take place. If it’s a completely new start of a discussion, that should be a new thread.
All of these threads are looked at on a case by case basis and we (hopefully) choose that which makes the most sense or is the most appropriate thing to do for that particular situation.
This may possibly be bothersome to those who prefer that all rules be the same always but you know what ol’ Ralph Waldo said on the subject of consistency and zombie threads and when he’s right, he’s right. 
These pretty much sum it up.
In GQ, if a resurrecting post is relevant to the existing thread and provides at least some new information (or subsequent ones do), then there’s no reason to split off a new thread. If the new post is not useful, or the thread is otherwise problematic, it will be closed.
Offhand I can’t recall a case in which a resurrecting post deserved to be split off in a new thread.