I don't think he should be in the long-term plans until he proves he should be in the long-term plans.
It's one thing to be "in the plans" before you get a chance to prove yourself an effective (or ineffective) NHL player. Jack Quinn, for instance, is "in the plans" right now.
Mittelstadt, though, has proven to be mostly useless at the NHL level (and from what I gather, just OK at the AHL level, though our more frequent Amerk viewers can correct that statement as needed).
We can place blame for his ineffectiveness all we want, but it doesn't really matter. What matters is that he's proven to be ineffective.
Hopefully he can right the course. I'm doubtful.