95 blazer blown engine or not?

If anyone can help me I would very much appreciate it.
I was driving down the road going about 40mph when my blazer just dies I coast in along and park it. The tow truck driver eventually gets it started and it chugs and miss fires. He said it was blown and my machanic went with his diagnosis. My question is, is it blown or not? Could it be the timing chain? Can someone help?

Kinda hard to tell with the vague description. Could have bad rings, bad lifters, bad crank, sieze, etc...We need the info...