I've heard money isn't an issue with NR and it's just strictly due to passion, but I think losing money to a project you're not even into anymore is a bit of a bitch. He could at any moment turn the servers back on, but he's so branched from the project at this point he likely doesn't even want to bother with it. It is assumed Winter was able to turn on the servers and did so, but it was turned off soon after. I don't think anything has been confirmed as of why, but I kinda think that Nilly or some other admin asked Winter to keep it down to save on money. Nilly's Realm currently is a liability to Nilly, and he can't go on Discord without being harassed about it. A strong example of this is when Nilly attempted to get into Overwatch awhile keeping up a connection in Discord, causing people to joke and make fun of him awhile spamming him with @mentions. This is very likely the reason he doesn't really show up and why the servers remain down to this day.
Again, this isn't information confirmed by anybody with close connections to nilly, just speculation that isn't too unlikely.