People blame Idzik for drafting Milliner because of injury history (even though he never missed a game in college). Should have expected him to get injured. People blame Idzik for drafting McDougle because of injury history and should have expected him to get injured. By that logic those same people should in no way want whomever to slate Vick as a starting QB -- but strangely in this case to them injury history means nothing.
That's probably because Milliner/McDougle both (a) cost a draft pick, and (b) had equal or better alternatives available. Frankly, there is likely nobody better available to replace Vick and he costs the team nothing (other than a minimal salary) to have him here. That's the difference.
I think you should wait a little more to worry about this... there's still a good chunk of the season to play and a lot of things can happen, Vick can slump, get injured or if the Jets fire the actual staff he may not be a good fit in the new regime's offense or whatever. I'm not saying any of those things will happen for sure but it's a little too soon. And about drafting a QB early and having him holding the clipboard while a vet is on the field, well, it may happen this way but if you look at recent history there's a much bigger chance the rookie will be starting right away or at some point early into the season. How many 1st round QBs have been backups most of their 1st year recently?