The issue with the coil is irrelevent, they were just trying that one on.
Many engines will never have a problem with the shells after a cambelt failure. It is however concidered best practice to replace shells. It is in the Alfa Romeo procedure after all as you have found out. At the very least the customer should be informed of the risks assioated with a repair of this nature. In many cases it is better, or safer to replace the engine than repair it.
The real issue here is, regardless if the bearings were inspected or not, they did not inform you of the risks assioated with fixing the engine for you to make an informed decision. So they are liable for that decision. Also, if the bearings were inspected and replaced this would fall under their waranty. It is unreasonable to omit part of the official procedure and then deny a waranty claim because of doing so.