I suppose you can keep running it as is. Leave the reservoir pressure cap loose so it doesn't keep puking coolant. Something's going on that the pressure and compression tests didn't fix. Seeing as no one's going to recommend repairing a cracked or severely warped head, there isn't much to lose by driving it until the engine quits. Hopefully you have enough warning of impending doom that it doesn't leave you stranded.

Sixto
87 300D