So let's say we're like 9-10 weeks into the fantasy season, and Owner A has been able to make trades all season long. During Week 1 he told his opponent that he wants to go all-in this year because it is likely his last year in the league. The opponent thinks Owner A also told him this during the off-season, but isn't 100% sure. However, Owner A has now been eliminated from the playoffs and it does seem like he will not be coming back to the league next year. Sure, he might come back next season (the previous season he said the same thing, yet still returned), but odds are he won't.
This is a dynasty league where, obviously, you can trade draft picks from future years to acquire players. Owner A has made these kinds of trades with the Commish and other owners all year, even after Week 1 when he told his opponent that he was leaving. There is no trade deadline and teams eliminated from the playoffs are not locked from making roster transactions. In fact, trades have been processed to teams in the championship right before kickoff for Week 16.
So do you still allow Owner A to make trades, or do you shut him down completely?
Assume that the league does not vote on trades, but that the trades he will make will be for fair-market-value (as determined by many previous deals made in the league).
Also, keep in mind that somebody else will have to inherit his team, but the new owner has not been found just yet.
However, also be sure to consider that Owner A has paid full dues for the league this season and that the team is still 100% his at the moment.