We have no idea if/when Fred is leaving and who will replace him. Your level of speculation is ridiculous.
IF Fred decides to leave within the next few years, TJ will likely be on the shortlist for obvious reasons. Nobody knows why TJ came back to Ames, maybe it's just because everyone knows Washington is going downhill and ISU is a top 10 program though. It's not always some kind of crazy situation where we're hiring a coach-in-waiting.
But look at these factors and it just seems to make no sense why TJ came back:
-Iowa isn't close to his roots in Wisconsin
-He didn't spend 6 or 7 years of his life in Ames so he has no idea what life is like there
-His wife has no connection to Ames or ISU
-He's never been successful at ISU
-He and Fred have ZERO prior history together
-We're not going to be very good next year
-He's not making very good money
-This program isn't rising or back
So with that said it all adds up that Fred is leaving and TJ is the next coach, that is the ONLY thing I can think of that would draw him here, he probably already has the guarantee and Fred is just sticking around next year to keep up appearances. TJ will probably be doing most of the head coaching duties to get ready for the transition I would assume.