Saban wouldn't leave Bama for Cleveland for 30 million per year. Not a chance.
There are loads of examples of players and coaches putting their legacies on the line for a last challenge. Gruden is doing it right now for the Raiders. He has his ring. He's generally regarded as a very good coach. He could have had that Monday Night gig forever. He was itching for the challenge again.
Pete Carroll took a risk going to Seattle from USC. Things fell apart at USC but he could have done TV for a year and then picked his college job. With his USC success he would have recruited a ton and turned any college team into a winner.
Plenty of college coaches have risked legacies to prove themselves in the NFL. Chip Kelly left Oregon. Lou Hotz tried his hand at the NFL. Bill Walsh came back to coach at Stanford.
Jimmy Johnson left Miami at the height of their dominance for the awful cowboys. Spurrier did the same leaving Florida for the Redskins. They are probably the best analogy to Saban.
I doubt he'd take it, but it's not crazy. He'd surely get full GM control. They have a good OL. Good RBs. Possible great TE. Defense has a stud pass rusher, Denzel Ward looks like he'll be a very good cover CB. As i said, if you think Mayfield is good then the Browns is a great job. Only a few players away. Look at how fast the Rams went from dumpster fire to great with the development of Goff and some good coaching.
The Browns have tried everything. They've hired a college coach. They've hired retreads. They hired a guy off the Patriots staff. They've hired assistants. None of it has worked.