When you donate to a server (via paypal), you are donating to their paypal email...
So you have their email address... Use this to send them a message and ask any questions you have.
1st of all, you should verify if the server is temporarily offline for maintenance ? Or if it's permanetly offline ? And if the server has been shut down forever... then ask the reasons.
Now, if you want to request a refund... then your request should be reasonable... If you donated, then played on the server for more than two month... then it's NOT reasonable to ask for a refund after two months...
If, however, you donated yesterday, and you just find out today that the server will be permanently shut down... then that is more reasonable request.
Now, if your request is reasonable, then the owner should honor your request. But if your request is totally and completely unreasonable, then expect it to get denied.
If your request is reasonable, and you get denied a refund... then just do a reverse DNS lookup on vanillapvp.no-ip.net... It might be their home address... then just threaten to DDoS attack his internet and bring it to a screeching halt if he doesn't refund the money.
But now that i think about it... another possibility... all no-ip addresses are FREE as long as you update them every 30-days... either manually, or automatically with their program. The situation could be as simple as, the owner was so busy that he forgot to update his DNS and it expired after 30-days... If this is the case, the server is still there... you just have the type the numbers instead of the DNS.
At any rate, you should use the paypal email address to contact him and find out what's going on.
Good luck !!!