Honestly, if you guys all stuck on Vornskr until we were forced off, I'd do the same since in the end you are the only guys I care about anyway.
As far as I know, most of the high leveled members of TWC will move to The Harbinger, and the guild will be reopened on that server as well. I think that that is the best for the guild and its members. We get a more active server and the Casual Alliance, which TWC is part of, will move as well, which means we can still team up with members of the small guilds within CA to do Ops with (which TWC can't do on its own).
Vornskr won't be decommissioned or merged for some time (I think), but it's obvious that its population will decline after this transfer and a lot of TWC members will not be found on this server anymore. In my opinion, it's in everyone's best interest, then (certainly if you want to do endgame content with us), to move to Harbinger.
It's also possibly the only chance at a free transfer you'll get, so if you mean to transfer anyway, best to do it now.