I agree with Champions and Dylan that it mostly comes down to Donnal's own play and what those other three guys do. But my guess is that if Beilein sees a potentially big Final Four type year, he's more likely to keep Donnal around. I think JB will be here another five years, at least, but he also knows there's no guarantees. Having Matthews here ups the chances of '17 being a big season (vs, say, the other '17 recruits not named Wilkes or Jackson), and therefore tilts the scales a bit more to keeping Donnal than ensuring Teske and Davis get opportunities to develop.
Again, I'm not saying we don't take recruits we really like to keep him, but it (a) makes it less likely we'd just let him walk like Spike and Max, and (b) might make us a little more hesitant about a guy we like but don't love.
But I'm clearly outnumbered and other folks are probably more plugged in. My main point is that with Matthews in the fold, '17-18 is looking pretty darn solid and potentially very, very good 1 through 4.