I believe I read somewhere that Wyc said he had to borrow money to finance his share of the club. Irving is, in essence, the Grousebeck family since Wyc and siblings stand to inherit his wealth. That Irving designated Wyc to be the managing partner (i.e. the 'owner' in the eyes of media and fans) makes sense.
To me, the easiest path forward is to reformulate the partnership and replace Irving's money. Wyc could very well still have equity in the team once completed. The problem would be if someone from the outside comes in and outbids everyone else by a huge margin. It is not often that marqee sports franchises like the Celtics hit the market.