I agree that they both need to play, but I don't think this is that hard. Arraez is the 3rd Baseman next year for 80-100 games, plays second to give Polanco a rest for 20 games, DHs a few, plays LF for a few, and is on the Il at least once with his balky knee. He winds up playing in about 125 – 140 games. Donaldson simply isn't the same guy in the field much anymore because he can't really move, so he winds up DHing 100 games and playing 50-60 games at 3B next year. Frankly, I wouldn't be too surprised if he thought about retirement because of his physical ailments and the Twins worked out a settlement of his contract but I'm probably being a little optimistic there. With Donaldson as the primary DH though, it does make things a little interesting with respect to Sano, Kirilloff, Kepler, Larnach and Rooker. It also pretty much eliminates a Nelson Cruz revival, although I don't think that was a likely scenario anyway.
Bottom line, next year I would really like to see the starting lineup with Polanco at 2B, Arraez at 3B, Donaldson (or Cruz) at DH, Sano at 1B, a new SS, Kirilloff in LF, Buxton in CF, Kepler and Miranda platooning in RF, with Miranda also backing up in the infield, a Garver/Jeffers catching combo, Gordon as the IF/OF utility player, and a fight to the death between Rooker, Laranach and maybe Astudillo for that last spot on the bench. Losers go to AAA as the 27th and 28th men to join Cave, Refsnyder and Contreras as players in waiting.