Was driving my 300tdi at 70 oblivious to the world and didn't notice the engine overheat until it was too late and the engine died and I notced smoke out the back, Lifted the bonnet and plums of smoke, not good.

Got recovered home tried to start and nothing, cranks but no fire. Could this be a simple head gasket or could I be looking at more extensive failure?

Any help much appreciated

You'll never know until you get the head off. It could be a warped head, cracked block or you might get lucky but I suggest you find the reason it overheated first