If a rider unilaterally breaks his contract, then there is no contract to buy him out of (which is the question that Ingsve asked).
I would hope (but do not necessarily have enough trust in the UCI to assume) that in such a casse then there would be strenuous investigation as to the antecedents of that.
If (lets remove real names) Jack Peddeller suddenly resigns from Team Respectably-Average and comes to a settlement with them over the remainder of his contract, and then 2 weeks later signs for BigCashR_Us Pro Racing, there should be checks as to whether BigCash had spoken to Peddler or his agent Mickey Fingers before that shock mid-season resignation. If it is found that there was contact, then BigCash would have a 12 month embargo on making signings, Peddeller would have a three month suspension*, he and Fingers would be fined up to CHF 150,000 each, Fingers would have his licence suspended, and BigCash would be fined 1.5M (article not quite clear on the amounts of the fines). The article is not clear as to whether the new contract with BigCash is considered valid or whether Respectably-Average would receive something beyond what they agreed with Peddeller.
* :
@search would have to decide how that effects his CQ game price the next season