Considering this has been a problem where people ruin a salary cap for a team and here is a recent example (
https://nfl14.myfootballnow.com/community/1/5342?page=1#32286 and
https://nfl14.myfootballnow.com/team/12 ) then really when people screw a teams salary cap they cant abandon that team either thru abandon team or after the 21 days and where they cant even join a new league either until that mess of a team is fixed and if that means they have a team for 3 seasons or 4+ seasons then so be it.
Basically this is a 3 step program
1)If you screw up a teams salary cap you cant abandon team either by button or after 21 days
2.) if you do #1 you cant join a new league
3.) so basically those people will have to learn the hard way if you mess it up you have to be stuck with that team for the foresee future until that team is out of salary cap trouble and/or that team can contend for the playoffs.
basically it forces to make sure they want to do that to that team knowing they will be stuck with that team and maybe make them think twice about messing up a team's salary cap