This is an awesome mod. I have a couple issues and a suggestion.
If you fall off the edge of the world into the void you will get an error and be disconnected by the server. My assumption is because it is trying to create the tombstone at an invalid location (Y=-200 or wherever you end up dying) I think this could be fixed by doing a check on Y in the DeathEventHook.java for Y < 0 and setting it to some arbitrary valid value like 45 or 64 or whatever. So you could still get your items even if you have to dig for them or build up to them.
Something else I have run into is if I am taking items out of the tomb stone and die again the item I just picked up will go poof. I suspect the item does not get dropped by vanilla and is not considered in my inventory yet for the purposes of the tomb stone inventory loop. Maybe a check can be done for a picked up item along with the inventory loop? I have no idea. But since you are going back to the place you just died with none of your equipment, death isn't too remote a possibility and this does happen.
A nice feature to add might be if you could configure and override the vanilla XP loss through a config file. It would be nice if it could be set by the server admin to 1/2 or 1/3 or 2/3 or 0 as opposed to the strange penalty applied by the vanilla code (where the dropped XP is essentially capped at 5-6 levels no matter how many levels you had when you died). I guess this was originally implemented by vanilla for lag purposes, maybe before they had the bigger orbs. I don't see it being a problem now since you could create a few orbs of whatever size. The XP could even be put inside the tombstone with the bottles of enchanting.
