You know KHL rules, but you have absolutely no clue about contractual obligations between Radar and Magnitka and when it comes to credibility I'm sorry but I'll take the word of a person involved in the whole proceedings (Radar's agent) over yours.
Vorky may claim to have an understanding of KHL rules, which is fine. But I have an understanding of the US laws, and if the parties had an understanding and agreement, even if verbal In nature, then a contract was likely formed. If the contract is breached, O'Reilly will have a host of legal remedies to pursue, regardless of any MOU currently in place between the leagues.
Both from a PR and legal perspective, it would be a real mess for the KHL to try to avoid the verbal agreement reached between the parties. Of course, this assume that O'Reilly's agent is able to provide evidence of the verbal understanding. If he is a lawyer, which I would assume is the case, that should not present much of a problem.
The situation could get messy depending on international conflict of laws principles. Perhaps Russia would try to assert its laws applies, but O'Reilly is a Canadien citizen employed in the US (affecting US employment matters). Canadien laws may be the proper jurisdiction for the applicable laws, and I believe that a similar conclusion would be reached.
The point is that if O'Reilly and the club reached a verbal agreement on an opt out and the KHL refuses to acknowledge it, I believe it would point a lack of intelligent leadership by the KHL and it's constituent club. The negative consequences of such an action would be too great to take such an action IMO.