Hi Larki,
I'm sorry to hear about your situation, that is indeed the worst situation a cadet can be because the MPL licence does not give flexibility to apply for a different airline or look for any job (bush flying, banner etc). That will require extra training/conversion, extra money and extra effort. For many aspiring pilots a MPL route is 'better' than an ATPL route due to the conditional job offer and many, if not all, will chose MPL route if that is offered. From this perspective your son has no fault in this and he must be supported.
For this reason I think EZY together with the training organization must do everything possible to ensure a future job for your son (when the situation will be better). That means even if there might be a pool of highly qualified pilots when the market recovers, EYZ should first honor the MPL contracts.
I think you should stay in close contact with EYZ/school. We all know the situation will eventually get better, we just don't know when. Different people have different opinion about time, but the reality is no one knows when market will recover.
On the other hand, having in mind the circumstances, EZY could not have continued the training (like any other organization/business in Europe) due to lock-down/social distances and due to the lack of jobs they can offer in the near future. However I am horrified that they have canceled/void the training/contract instead of delaying it.
For the avoidance of doubt, did EZY cancelled/abandoned completely the training/contract or they suspended it for the moment with the intention to resume back when situation will get better?