Is my CR30 dead or...?

Lent my 2007 Y61 3.0CRD to a mate.
He put unleaded in it, drove it for about20 km.
Parked on his driveway.
Then it wouldn't start.
3 weeks later I worked out he'd dosed the engine.
Manual fuel pump bowl refused to pull anything out of the tank.
Towed to local mechanic who confirmed diagnosis, drained the tank, changed the filter.
Got it running.
BUT
Mechanic tells me that the return to the tank from the CRD is too strong and is bursting the lines.
To me that sounds like the pump is doing its thing but the injectors are buggered.
Its the local servo mechanic, not a diesel specilaist.
I'm in Canberra so we we pay 3 times the price for half the service
Only has 135,000km from new (I bought it new).
Any info/sugegstions appreciated.

Or that its the wrong fuel filter

I am wondering if the return lines are blocked, or the hoses have reacted and swollen, closing up the bore. The return line to tank is basically an over supply relief line, so don't think it has anything to do with injectors either. The same thoughts for the supply lines that are probably collapsing partially under vacuum trying to suck fuel out of the tank. Does your model have a lift pump to assist the flow from fuel tank to injector pump? Sorry, these questions may be obvious to some, just trying to eliminate possibilities. I would seek advice from a diesel specialist.

@NissanNewbie is the bloke to ask.

Give Dave at cooma Diesel a ring . He will put you on the straight and narrow . !

Whats your mate doing about this ordeal?

This sounds like a nightmare come true, I’m guessing he drives a petty car and just forgot he was in a diesel. I have a petty and a diesel so I always double check what I’m doing. Skyline with diesel wouldn’t run well and td42 with petty I’d probably cry