On the one hand I agree it seems wrong to keep money for which you do not end up providing the services that were bought with it. Maybe he could donate it to a charity helping the Ukraine.
On the other hand, anyone who knows how business works in ex communist countries knows that this is a common and accepted part of the risk of business there. I doubt very much Mr Mazepin has honoured every one of his business contracts. In fact I would say it is impossible to become a billionaire in Putin's Russia without breaking a few contracts, and probably much much worse.
These guys are not nice people, have no morals and are very exploitative. I really wouldn't feel too sorry about Mazepin losing a bit of loose change to an F1 team. He's done far worse to others for sure.