Yes you do apply to another airline, as simple as that. After paying £105 000 the get an MPL with an airbus rating. So lets hope another airbus operater will take you on and not bond you again for line training
I can't really see what the difference is in that respect from any other cadet programme? If you did an integrated fATPL programme leading to cadet airline placement, you may or may not have spent the same amount of money, and the result would be little different if you were terminated with 600 hours.
It would be quite unusual to be bonded for line training? Such bonds are normally for type rating training. Although there is a cost element to line training, it is conducted on revenue flights as a rule, and although specific to the number of available training captain tracks, additional resource (safety pilots) is usually limited. In any event, for the hypothetical case of somebody transitioning with 600 hours on type, the line training wouldn't usually be any greater than for anybody else with experience on type.