The answer to such a question starts with "anything is possible".
That said, for ANY team to go undefeated, an incredible amount of luck is required. Having a "chance" to go unbeaten, is a measure of how good a team is...but actually doing so requires much more than just being good.
So you could more easily argue for Iowa being the best team in the nation...than you could reasonably expect them to go unbeaten. There are just too many factors in play on any given Saturday...regardless of how good a team may be.
As for the Hawks...even with Bulaga back...there are still a number of question marks along the offensive line. That is a potential weakness that must be fixed...and it may well be in the off season...before talk of National Championships can be taken seriously. The loss of Calloway, Richardson, and Eubanks WILL be felt...it WILL take time to get the new OL up to speed...IF it gets up to speed.
Further, while there seems to be much talent and potential...replacing Angerer and Edds will be tough as well. Less, perhaps, from a talent perspective than from a leadership/toughness point of view.
I don't mention these issues to be negative...every team has issues/shoes to fill as it enters a new year. And every team will address those problems the best it can...sometimes affirmatively and sometimes not. Its virtually impossible to know ahead of time how that will work out...there is much reason for optimism in Iowa's case but there are no guarantees, even in cases where there appears to be talented replacements.
A football team is mixture of chemical elements....every alteration in that mixture can end in a new and unique compound. Which brings this discussion back to....ANYTHING is possible, including a National Championship.