Let me say i am not sure if this game does this already when a person leaves a team everything gets reset so if this does please disregard this idea.
That being said my idea is to have a reset/factory reset where either if someone leaves a team they can hit the reset/factory reset button or the league admin if it is a created league can hit the reset/factory reset button.
*that way persons contracts get cancelled for players
*same for coaches
*same for trades
*same for their gameplan
*etc.
Basically they cant ruin a team or someone thinks they ruined that team
just a thought