377209 did return to Southern last week, was on depot for a little bit. It's all going down to the last minute with the cascades and moves.
In theory the 377/7s should have arrived and been commissioned with Southern, which would release 6 377/2s to go from Southern to FCC, which in turn would release some 319/3s to go from FCC to Northern.
However, no 377/7s have been commissioned yet, so it would be difficult at the moment to release the 6 377/2s. Fortunately, no 319s have moved yet so nothing needs to cover them.
There is a 319 move to Northern planned for this Thursday, which if it goes ahead will leave FCC one short (possibly two short given the unit that got damaged recently). I don't know, but a 377/2 may have to move over again.