You are forgetting about some of current guys too.
Cartwright has progressed significantly during the course of the year. Yes, he still forces shots and takes some ill timed ones, but his game is solid. He'll be better next year.
Devyn Marble has gotten better and better as the year has gone on as well. He could challenge for a starting spot in the lineup next year. He has the length to be effective and the skill set to succeed, just needs a little more weight. He'll get that 10-15 lbs over the summer. He should be a solid player next year.
Basabe is back and he has shown the ability to take over a game from time to time, as well. Bigs take longer to develop, so the sky's the limit with this guy.
Then you've got complimentary players like Gatens and May - both need to bring their games up next year. Gatens has been pretty consistent in his 3 years and you know what you are going to get. May needs to get back to his old self, someone we thought would thrive in this offense actually looked better in Lickliter's system. Hopefully he turns it around, he has shown flashes.
Biggest need is a center. You lose Cole and you basically have Brommer as a senior.
Also, you don't know about Cully, if he's going to be able go 100% ever again. So you have to go out and get another PG, esp with Bryce being done after next season.
The problem is, the PG and C are two of the most difficult positions to find when recruiting. They are hot commodities. Iowa is in on at least 3 solid PG recruits and at least 2 or 3 PF/C. If Iowa can get two in the spring, the Hawkeyes will be fine.
The current players will improve (we've seen improve just in-season, so there's hope).