In terms of choosing sides, i'd say i'd be with Rudy, but in terms of team management, i'd say that if forced to choose between one of them - and it really looks likely it at the moment - the right decision for me is to trade both (and all others) and rebuild from the scratch
Keep Mitchell and you take a step or two back, and, even if Rudy return allows you to a not very long road towards being back to the same level we are right now, till then, he already asked out
Keep Gobert and maybe winning percentage overall you could take a smaller hit, but at bare minimum you lose a closer (hardly receiving even a potential one back, even more if he goes on "i wanna be traded to here, here or here, and won't re-sign out of these places) and top playoff performer, taking you further from being an actual contender, and a package around him would come around young players and picks that even if they pan out to be a home run, most likely, the time to them get good enough to lead us, it's Rudy that will have peaked and starting his downfall