Usmanov has the shares already. Why would he "continue to pay" a penny for them?
Kroenke has all the control here. Even if Wenger goes, he can run the club in the exact same way - don't put a penny in and don't take a penny out. Let the CEO and the manager take care of rest of the details.
There is absolutely nothing Usmanov can do about anything here. In fact, it is actually hard for him to even sell the shares and get out because no-one else would invest so much of money in something that won't give them the control of the club and Kroenke would buy them only if he is selling at a very low price (or might not buy them at all).
Kroenke has more than 60% of shares. That gives him control of the boardroom and as long as he is happy running the club the way it is being run now (without any major changes like new stadium or huge investment somewhere etc) he doesn't need Usmanov's support.