Interesting question, Steph... though I hope you haven't already asked and answered it in your OP!

In my experience (I'm old and come from a very large extended family -- mostly Catholic, but also including a good brushing of other religions, and no religion at all -- have been to a substantial number of funerals, and have personally endured -- and seen endured -- the loss of many close friends and relatives), I've found that true believers, folks who hold their beliefs in their hearts rather than on their sleeves, actually do tend to have very short periods of grieving.

Yes, the things you already talked about, like survival instinct and personal loss, are certainly immediately present, and grieving can be profound, but people who hold deep faith in an afterlife tend to become, well, comfortable, in the loss of their loved ones. True believers really do come around pretty quickly to the confident understanding that their loss was the deceased person's gain, and they will indeed be with them again in person one day, and can communicate to them through prayer during that wait. Yes, those instincts and sense of personal loss will well up on occasion for years (or life), but they are quickly salved by that confidence.

The only exception I've seen in this is a parent's loss of a young child, to which there is no recovery.

tl;dr: In my experience, a positive view of the afterlife does seem to prevent deep grief, at least after the initial shock wears off.