some other possible solution would be to
a) with the engine stone cold, put some penetrating oil on the bolt and let it sit a while
b) take a light weight hammer and whack the bolt a few times to help loosen it
c) take a chisel and score a line through what remains of the bolt to provide a contact point.
Then either use the chisel to move the bolt, or a vice grips, or one of the methods mentioned above, or drill the bolt and use an easy out.
If there is a fair amount of metal on the bolt, you could drill through the side, and insert a screw driver or similar small and hard piece of steel to gain some leverage.
You could also use a sawzall to cut a couple of straight sides onto what’s left of the bolt so you can get a better grip with a vice grips
Hope this helps…!
'00 ML320 "Casper"
'92 400E "Stella"