I was wondering about this cause our Kappa Phi chapter recently came back to Mt. Union College. Tri-Delta had left maybe 6 years ago...we left slightly earlier, in, oh, 1910 or so.
I had thought the school would instantly go back to DDD for the alum support factor, since all our alums from that chapter would be quite dead, but they asked the 2 of us (along with KD who also had been there) to present and picked us. Whatever, I'm glad they did.
Cream, I think the 4 year wait you are thinking of was to assure that all the present members have graduated. Of course since graduating in 4 years is far from the norm anymore, it's now usually wait until after all the present members graduate. One of the fraternities that had been at my school wanted to do this, but the old brothers just kept...not graduating. (they were not the brightest bulbs in the chandelier) I think the national finally gave up.
It depends on the Greek advisor too...sometimes if who is in that position has changed since the chapter originally left, it can also be an asset.