It's not a big leap. If we play Akron, we beat Akron. With the first game jitters out of the way, we beat a Colorado team we almost beat anyway. Maybe that carries over to Troy. It's the same team that would finish 4-2 with a close loss to #8 Ohio State, so 6-6 wouldn't have been unlikely and Frost would have met the minimum expectation of returning the Huskers to bowl worthiness. As it was, everyone was optimistic enough about that 4-2 finish to rank Frost's Huskers as a sleeper Top 25 team the next year. Now that you mention it, the trajectory probably wouldn't have changed at all.
Never heard that Kalen DeBoer would have seriously been considered in 2021, as Husker fans would have thought a coach with only two years at Fresno State was unworthy of our legacy and aspirations.
Biggest deal is if the Colorado chump doesn't intentional twist Martinez's knee, that game and the next couple look a lot different.
Frost had plenty of failings. But he also had about the worst luck of things (like the two talked about here) there were completely out of his control.