The second half of the season is time for Buxton to get back in CF. The team can get the same offensive production by rotating other players through the DH spot, but the defense improves by having MAT as the backup CF instead of Castro.
Yes Buxton is league average at DH (101 OPS+), but MAT is not league average in CF (82 OPS+). Kirilloff, Julien, Gallo, Jeffers, Solano and (SSS) Wallner are above average OPS+. Lewis, Correa, and Polanco could all have a "day off" at DH. As could Miranda, and a "day off" from the glove could help his offense.
If Buxton gets hurt, MAT goes back to CF and the others can continue the DH rotation.