Hi,
Just going put in my 2 cents
A motor gets hydrauliced because the piston comes up on compression stroke with both valves closed and encounters an uncompressible liquid.
Just the inertia of the spinning flywheel and the power of the starter (with all of its gear multiplication) is enough to do damage
The valves are closed so they can't be bent and the part that usually fails is the bending of the connecting rod.
If the piston is coming up on the exhaust stroke it bends valve stems or bends push tubes as the piston is coming up and compressing the liquid the valve is trying to open against it as well.
If you want to gamble that the bent connecting rod will stay together than you can run the engine and take your chances or you can do the safe thing and pull the motor apart.
If he has run it for 45 minutes already it it most likely no major issues plus if it was a bent rod it would be running like crap and vibrating a shaking like heck.
With a hydrauliced engine the damage could be a bent rod, collapsed piston, bent wrist pin, cracked main bearing bulkheads and the list goes on and on...
I think that you should do the safe thing and not run the engine again and disassemble it to check for damaged parts...
A compression check will tell him a ton along with an injector test.
Even if it is something major to repair it would still be cheaper than replacing a blown engine....
Not always, a lot of times it is cheaper to replace and engine versus pay shop labor to verhaul unless one does his own work.
Like they said in the old Fram filter commercial "Pay me now or pay me later"
Running Fram filters will cause you to pay in the long run anyhow
It all depends on the amount you pay
Good luck with whatever you decide,
Bob