This is utterly shameful. These cadets have been hung out to dry by both their training school and their prospective future employers. At a time when Airlines are taking government loans (that are being written off) in order to keep them afloat, this is how they choose to treat those who have made a commitment to work with them. As noted above other options have been taken in the past. This is no way to treat customers or staff, and nobody should forget that. Cadets have not had a voice for a long time and hence the rising cost of entering the industry, but this treatment is beyond the pail.
I think these cadets should take legal advice. It is against the law for any company to abuse a dominant position in the market, it is also an anti-trust issue to tie sales of products when in that dominant market position.
These are difficult times for everybody, but for a corporate to dump the entire risk and impact of this situation on a vulnerable (and easily bullied) customer base is nothing short of shameful!