Well, last season, ISU went 7-6, with a win in the Insight bowl over Minnesota. They were 6-6 regular season, and 3-5 Big 12. However, you really have to consider a couple things.
1) Their non-conference schedule last year consisted of Kent State, Army, North Dakota State and Iowa. This year they face Northern Illinois, Northern Iowa, Utah and Iowa. Northern Iowa has beaten ISU, and nearly beat Iowa last year. Utah's pretty good... Point is, while last year ISU's non-con record was 3 solid wins and 1 solid loss, they don't have that sort of 'guarantee' of wins this season.
2) They replace Baylor, Ok State and Tx A&M with Texas, Oklahoma and Tx Tech.
A&M may be better than Tech this year, but Tech is still pretty good. But point is, ISU only has so many "probable wins" this year, in NIU, UNI, Kansas, perhaps Colorado or KSU. That's only 5 wins. You already need an upset of sorts just to make it to 6 wins. Lose to NIU in week 1 and you're going to have to upset two teams to make it to 6 wins. Not impossible, but definitely not the pressure you want to place on your guys just to reach 6-6.
The one thing we have going for us with this schedule is that the tough games that are winnable are at home or neutral. Nebraska, Missouri, Texas Tech, Utah, KSU. All at home or at a neutral site. I think if we start 1-2 with a win against KSU, we still have a good shot at 6 wins. Less margin for error, sure, but still a good shot. That's why I don't think this is a must win from a fan's perspective.
I would say that we need to win at least one of NIU and KSU.