What did you pressure test? Cooling system, I’m guessing, but maybe a compression test?
If the cooling system won’t hold pressure, I would guess a warped head and head gasket failure. That probably means coolant in one or more cylinders. Be cautious of hydrolock and doing more damage. A soaked cylinder may not be an issue, depending on whether rust has started to set in. I’d first verify that the pressure leak is in the engine, not the heat exchanger or some other external part. If it’s confirmed to be in the engine, then get the head of pronto and get any coolant cleaned out before you get rust. It may not be a huge job to get it working again.
BTW, I wouldn’t be surprised if this is covered by your insurance.[/QUOTE]
X2 on this comment! You insurance should cover the damage, and the good news is they probably won't fool around with trying to "repair it. They will just rebuild the entire engine. Also, if the transmission is turning, but not being cooled, they might end up replacing that as well.
Pro: You could very well end up with a "new" engine and transmission for the cost of the deductible.
Con: You will have an insurance claim on your record, but it should be covered under "comprehensive", so may not count against you too badly.
Best of luck in whatever you decide!