I do think the JSA (and Legion by extension) will be back at the end of Clock, and maybe the Kents (or at least one of them) unfortunately, but that leaves a number of other loose ends that need to be tied up.
And no matter how this gets resolved, it's going to result in a new continuity. Even if it's heavily post-Crisis there's still a number of things that won't line up with that continuity that'll create substantial changes (Wallace/52 Wally, Jon Kent, etc). I can't picture DC adjusting their whole continuity without making a big deal out of it.