Martin has some immaturity and accountability issues overcome. From that standpoint, Iowa can definitely walk away without much concern.
However, now that the 2020 season has been canceled, the loss of Martin is significant to future depth chart. Brandon Smith and Smith-Marsette are both 3rd to 5th round draft grades. B. Smith might actually test off the charts at the combine. That means both those dudes have played their last snaps at Iowa. If football is played in the Spring, they both will sit out. Considering they're both on target to graduate this Dec or in the Spring, there is no logical reason for them to return with NFL jobs waiting.
Iowa will be forced to start Petras in 2021 without two experienced and talented receivers. Alaric Jackson will be gone to the NFL as well.
Martin would've had a great chance to become a focal point in the 2021 offense. His departure will be felt next season.
What's odd about him coming to Nebraska is the Huskers WR depth chart which sucked in 18 and 19, exploded in numbers for 20 and 21. Martin has more game experience than a lot of those dudes, but you have to wonder if he's willing to accept competition. I'm skeptical.