There have been some court cases regarding this matter in Sweden and Denmark. This is from the top of my head;
Sweden:
The Swedish Labour Court (Arbetsdomstolen) has had some rulings regarding the enforcement of training bonds by the military service. The military service didn't ask for all costs but only for a reduced cost of something in the region of £20.000. This amount was reduced depending on how long time the contract has lapsed. The employee actually got a higher salary because they were bonded, but only in the region of £100 per month.
The rulings have been that the military service can't enforce the training bonds. The only thing that happened is that the employee needed to pay back the extra money they earned because of the bond.
Denmark:
The Supreme Court of Denmark (Höjesteret) has had some similar court cases as mentioned as of above. The main difference has been that the value of the bond was more, maybe in the region of £100.000. However, this fee did still not reflect the actual cost of training which was much higher. There was no extra money paid only on due to the fact that the employee was on a training bond.
The ruling was that the employee had to pay the money due in accordance with the contract of employment.
As usual, the Swedish labour legislation, as well as the interpretation of it, is almost always in favour of employees that neglect one's duties. If I apply for a job I intend to follow any training bond signed. In countries like Denmark they will put me in favour of those applicants not intending to follow any bond agreement signed and hence not signing it.
If training bonds can't be enforced, it will not benefit helicopter pilot aspirants. If the agreements can't be enforced, operators would be more reluctive to sponsor employees and they have to gain all ratings on their own instead, and just hope that they will get a job at the end.