Gage Gubrud did what was best for him. The Eagles had already moved on with Barriere, and no one can fault how Eric played when he got his opportunity. If Gubrud had stuck around, he certainly would've seen minutes, but it would have put the coaches in a weird spot with two seriously talented QBs. Plus, although each guy is similar to the other, it would've required two fairly different schemes offensively that would've been hard to maintain. You can find evidence for this in how much better Eric played when Gubrud officially became out for the season and the offense was retooled to fit him (and that's great coaching, btw). The Weber game, with Barriere running the Gubrud offense, was our only real disasterous outing on offense all season.
Given what Gage accomplished, being a part-time QB (it probably would've been like the Padron / Adams year where each guy started a few) wouldn't have been what he needed to take it to the next level. WSU presented him that opportunity, and I'd be absolutely shocked if he isn't starting week #1.
The only way Eastern really gets hurt by this is if Barriere gets injured along the way.