What would you do?

A potential Secondment at a MNC Client was pitched to a friend of mine by his employer (also a MNC), about which he was very excited. In his current role, he's due to become Manager in 6 months (giving him a 38% hike), however none of his Bosses have given him any assurance to the effect that the promotion will be granted, but still he's confident that he shall get promoted. His name was proposed to the Client for the Secondment, and he cleared technical interview rounds with the Client's team. The JD shared by Client which position was being filled by Secondment is of AVP with my friend meeting the experience level sought by the Client. The fee proposed by his employer to the Client is 5 times my friend's salary and his ultimate plan was also to transition out from his employer to become a permanent employee at the Client, once the Secondment period of 6 months gets completed.

Now for reasons best known to the employer and Client, it is looking like the Secondment may not happen after all. In such a situation, what should be the ideal strategy for the employee (Feel free to comment below and share inputs/insights etc) - Should he approach the MNC directly, offering his services and interest? Or, given that the Client and his employer have an existing relationship, and there's a risk that the Client may notify the employer of the employee's proposal - Should he accept his fate and move on with life? Would your answer change in such a case, if the Client itself seeks out the employee and encourages him to join them? Is there any other option in your opinion by which the employee may secure and not let go of this opportunity?