From a personal standpoint, I'm sorry that Dan has to move on, primarily because he seems like a very nice man and he is a vocal promoter of ISU. From a coaching standpoint, I'm not sad, because as I see it, this change gives ISU FB a chance to be better than just a mid to lower tier Big 12 team.
To be frank, I see the same fundamental problems today that I saw back in 1995, 1999, 2002, etc. DM did not correct those problems, and that IMO is ultimately why he will be moving on. I don't know if it was stubborness in sticking with a certain philosophy, or if he just didn't know how to fix the problems. ISU football cannot move to the next level without fixing those problems, and I see nothing to indicate that DM would get them fixed in another 2 or 3 years if he couldn't fix them in 12 years.
Unfortunately, DM had no conference titles, no conference title game appearances, no New Year's day bowls, and 1 winning conference season in 12 years. Similar circumstances led to JO's departure, and good things happened in MBB after that. I'm hopeful that the same will happen now for FB.
I guess I've seen enough coaching changes among my favorite teams that I don't feel terrible after changes anymore. These men take alot of flack, but they are well compensated for their efforts.