Q: Is my engine worth fixing?

Drove Ford Mondeo 2.0 petrol hard on motorway for 5 hrs.

Within 10-15 seconds the following happened: began to smell burning, felt something "drop" in engine, engine began sounding rough, lost all power and pulled over to hard shoulder.

Flipped the bonnet and saw white smoke emanating for approx. 1 minute.

Got recovered to destination. Dipstick completely dry (not sure if ran dry or leaked after problem), added 2litres oil. Had to bump start due to jump leads not working although they spent 10 minutes connected to a working engine.

After bump start, engine still sounded very rough and irregular. Car began billowing massive clouds of white smoke (was nightime under streetlights so may or may not also have been blue), checked under vehicle and enormous oil puddle on ground.

My (non-mechanic) diagnosis: blown head gasket, leaking oil and coolant, possible misfiring pistons.

Does this sound right and is it going to be worth repairing for a vehicle that only cost £600.

My car has 144000 miles.
My car has a manual transmission.