No idea of the population on Runnyeye but you can still join it even if it is shown in red saying "Server Full". That is just an indication of current server load. If you don't mind which server then you might prefer to find a less used one but if you are joining friends then you can join a "full" server with no problem.
You question is a little unusual in the wording. The server is actually a game server on the internet (probably physically more than a single machine). The game cannot be played without connection to the internet.
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Wherever I go - there I am.