I don't understand the mentality of waiting until after NSD
If you leave right before NSD, you're putting the university in a tough spot (see - Kiffin to USC)
But if you leave right after NSD, you're putting the players in an even worse spot (both kids that signed at your old school thinking you'd be there and kids that didn't sign at your new school not known you'd be there)
As much as it sucks to deal with coaching turnover in the period leading up to NSD - as we know first hand - universities can recover and still put together a decent class. Screwing the kids seems worse to me.