buuuuuut Q never said it'd be deleted, that's just an interpretation.
Other interpretation: last posts+self destruction = the end of Q.
He's warning us about the incoming end, and how best to preserve his legacy, other than the screencaps and archiving we've been doing (fantastic job btw hardwork anons, no words can be enough to thank thee).
Be ready, of course (weren't you already?), but the whole it'll-be-deleted thing seems far from what Q said to me.