Did you hear any audible noise from the engine when it stopped? How many miles? Compression entering the crankcase can be caused from severe engine damage, such as a hole in piston. Check your cam & crankshaft timing marks, if they line up, pull valve cover and inspect camshaft for damage. Broken exhaust valve stem is a common problem with 1.9 TDI engines. Let me know what you find.
What were the results of the compression check before you pulled the head?
None known to me, remember,#1 rule Stick to the basics 9 times out of 10 its something simple, your diagnosis depends upon your understanding of how things operate. Take care