[Sophisticated Redneck]

Hope I'm wrong but it sounds like the engine is seized which can happen on the n55 after the oil filter housing gasket replacement If you do a Google search, you will find it appears to be a fairly common phenomenon In every car/suv this engine is used in. So much so BMW released a oil priming procedure for it. My theory is when doing the OFHG job there is a good chance the oil line gets airlocked somehow at idle rpm and above for the first startup as their procedure is basically pulling all your injectors wires and cranking the engine for 10 seconds, 20 second break then wait a minute and repeat the process a few more times. This would explain why the engine just stopped and then nuked the starter/relay after when attempting to jump it. Again hope I'm wrong for everyone who is involved but a quick way to find out is to try to turn over the engine with a breaker bar and socket on the crank by hand. I would do a quick search on eBay and the local yards for a used engine before you do just in case so you have answer for your friend if it does turn out to be seized.