Not an Everton fan, but I do enjoy reading your forum, so I figured I'd throw in my two cents...
Onana doesn't seem to be good any anything in particular; he doesn't score many goals, he doesn't have exceptional passing range, he doesn't assist/create chances, he doesn't dribble at an elite level, he doesn't make tons of tackles or interceptions...at this point he's all hype and reputation without any body of work to back up the belief he will be an elite player. It would be a good deal to get back what they spent plus any profit, because they definitely overpaid Lille; they thought they were getting Yaya Toure 2.0 but they essentially bought Papa Bouba Diop. If they can get him out for a decent fee and use that money to keep the financial difficulties at bay + hold on to Branthwaite, that should be the play, IMO.