I agree that the island won't let you stuff is hard to swallow sometimes. I guess it is similar to the idea of fate and fulfilling your destiny. It seems like the island has all of these people on a set path that it DOES NOT want changed.

We can assume that Mikael also has "more work to do" as the island has seemingly protected him from death many times...the protective fence, being shot in the Looking Glass station, etc

The people that have died (Boone, Eko, Shannon, Libby, Charlie, etc). I guess we have to think about what significant work they had done and the goals they had accomplished. Whatever their work was, it was done alright (as were they immediately after).