Synopsis: I'm sort of suprised that this isn't already a feature, or even a suggested feature, but I would absolutely love to see the ability to return to an instance / mission after going linkdead.
Possible Implementation: Given the ability to teleport back out, I don't see any problems with having the player appear as a ghostly form next to the group leader, and becoming active in the game 10 seconds later (thus letting you avoid dropping in to the middle of a battle unprepared, and giving you the option to teleport out if you'd like to).
You could also have a prompt upon returning to the game, asking if you'd like to rejoin the group. You might wind up in the middle of a fight and quickly dead, but still a lot more fun than restarting.
Finally, if you really wanted to open it up, you could give the team leader the ability to summon *anyone* in to an instance, as long as there was an open slot. This would obviously need to be consentual, and would probably involve a 1 minute easily-interruptable "activation" time to ensure it didn't get abused. Honestly, though, I can't see much potential for abuse - it's more useful to have had the person there all along, not summoning them partway through.
Reasoning: One of my friends has an internet connection that sometimes drops out every 5-20 minutes, and completing an entire mission with him is quite a challenge. I myself have a slightly unstable computer, and when it decides to crash three times on the same mission I and my guildmates start getting really sick of seeing the first half of the mission again.
M
