If they offer security him getting fired but favorable buyout clauses for him leaving on his own I actually think it makes a lot of sense for him to take the $$$ now. That's about triple what WMU can afford to pay him... so if he's worked out the deal right, I think it's a great move both short-term and long-term. No harder to win in Big West at Minnesota than it was to win in MAC taking over Western Michigan which was arguably the worst school in the conference at the time.
Do we know that there's a favorable buyout clause? Seems like a lot of years and a lot of money. Typically the higher the both of those, the worse the buyout.
Also, I'm not so sure that it will be easier to win at Minn vs WMU. A 10 win season at Minn would mean that you have to knock off some pretty good teams. If you inserted Fleck into last year's, Minnesota team, he would have beaten three of the following to have a 10 win season (PSU, Iowa, Neb, NW and Wisconsin). At WMU, you get get curb stomped by the two BIG teams you play each year and still roll your MAC schedule and get to 10 games and win the conference. In my mind, he was one season away from a big time gig. Now that's more like 2-3 years possibly because of the contract.
Also one nit, Cubit sucked as a coach, but Western has never and will never be the worst school in the conference. They are only three teams with better all time win percentage, they are fourth in titles won and Akron was by far the worst team on the field when Fleck arrived at WMU. I'm sure you just meant that WMU football was sucking when he got there, which is true, but I wouldn't use the term that they were the "worst school in the conference". As their facilities, history and potential will always be pretty solid as far as their position in the MAC.