yep, mine failed a few years ago. It was at 60mph so the damage was substantial. In my case, I had to replace all the valves, and as I wasnt aware at the time that the big ends would be damaged, they failed a few weeks later.. long story short I had to replace my engine.
Depending on how fast you were going at the time, you'll certainly have some bent valves, as Scottyf says, its an interference engine which means the valves and pistons 'interfere', if not timed correctly they hit each other.
I get a mechanic to do my cam belt but one thing i do know as others have said here, it must have cam locks, and the fact that your mechanic isnt aware of that suggests that it would be a grave mistake going there.. look for an alfa specialist.
Make sure you replace the big end journals too, or you'll be back at square one about 3 weeks after the top end rebuild.
I really feel for you, its a horrible experience and expensive. But there's always a bright side though.. you just have to find it... For me, I managed to source a very low mileage engine which ran perfectly. And i decided from that moment on, i'd learn as much about the car as I could so that these expensive mishaps wouldn't happen again..
These days i do most of the minor work on the car myself, suspension, services and other general work.. I researched oils and how they work, and pretty much made owning this alfa a hobby.. and its been great, the car is now mint and it keeps me off the street! (actually - I guess it keeps me ON the street! haha)
This forum by the way, is absolute gold.. without it, I wouldn't have been able to sort my car he way I have, and still am...
All because it blew up 3 years ago.