Well, considering the payment does go through (and in the situation you've said now, you'd recieve the payment) I would honestly keep it for your server, and when the payment does go through and you still have access, change root passwords / change details in files that he wouldn't figure out how to fix and remove everything that you've done.
You know, I honestly don't know why people pay such high prices for pservers, especially when it costs nothing to download eA and edit the files >_>