|The Blue Dude is Dead... Ghost Form FTW|
I like that idea a lot. One of the cool things about ghosts, at least in mythology, is the idea that the spirit refuses to pass on as long if it is leaving its work unfulfilled; I find that this would make a great hook for the players and provide a reason for you as the DM to turn your players into ghosts after they die, instead of simply killing them off. Let’s face it, your players are the center of whatever world you are playing in. They have some epic destiny that they are all headed for right from the get-go. So, why should they be allowed to die off?
Resurrection has been in RPG’s and video games for a long, long time, but playing ghost characters doesn’t seem to be nearly as popular. There are all kinds of mechanical problems that you have to deal with, especially with D&D 4e when you want to run a ghost as a PC, but, why not just ignore most of that?? I like what Demon’s Souls does with their ghost modes. You lose a bunch of maximum health and have penalties when you die in ghost mode, but those penalties are much less than those you would face by actually losing your real body and dying that way. If you dye while in any of the game worlds, you face a host of penalties including shifting the alignment of the world in a particular direction; if you get killed by another player, you might even lose stats because of that death, but dying in ghost form is just a speed bump. You simply need to go retrieve your body and reclaim the exp that is still hooked up to your corpse.
I think thematically, this fits really well with D&D characters. You have your destiny, it needs to be fulfilled, and not even death is going to stop you. 4e also makes it easy to implement something like the Demon’s Souls system – if your player dies, one round after he drops, let him rise up as a ghost. Make his or her max health equal to his or her bloodied value and maybe restrict them only to at-will powers instead of letting them use dailies and encounters and action points (hey, they did die); but, other than that, let them play as normal. Don’t let them walk through walls like Casper, and don’t let them possess people, but let them keep on keeping on. When the fight ends, a little spiritual jolt is enough to implant them into their body again and function, once again, as normal.
Try this method out and see how it goes. I think it might need some play-testing to make it fair (and balanced) but I think thematically, it could work fine.