The only "party wipe" grave in the game is the one next to the cheerful sheep in front of Thelyron's clinic. This is the only grave that will always kill your entire party, no matter how much health they have and how far away they are. This is also why the game gives you not one, but two opportunities to back away from the grave after attempting to dig it for the first time.
Other trapped graves in the game usually explode as an invisible mine at the center of the grave. You can usually avoid death by digging with a character who has high CON and fire resistance while the rest of the party keeps their distance - that's how I dug up every grave around Cyseal's old church without having to reload.
