Whether he goes or not could depend on his view of the current LV administration. He might not be so enamored with them as one might think, and that matters, probably more than money. I presume he is getting paid well at Purdue now, so maybe he goes from $2.5 mil to $6 mil or whatever, it might not be enough to compensate, perhaps maybe.
Or maybe they are thick as thieves and go hunting together, no idea. And if they hire someone else, there is a good change the position becomes open again in 4 years and in the mean time he might have built something notable at Purdue and be getting offers from "real programs" like even an Alabama. I don't know what CB wants from coaching. There is an inherent limit at Purdue and LV both.