Okay, here's the scoop.
Regarding reverse engineering: That's legal. Plenty of case law supports that, and we are actively doing this right now. In fact, we've been doing it for quite a while on the down-low in order to improve the quality of our third-party tools. We're hoping that things don't get to a point where this is the only option left. If we do, then we'll probably talk to a lawyer before we distribute any products of our efforts to make sure that we have the legal ammo to fight any C&Ds that NCsoft might fire off our way, though really, I kinda doubt they will. If we do release a server, it will almost certainly be without any City of Heroes IP included, as we wouldn't have the rights to do so. We've been internally discussing the option of releasing "content packs" that would replace all of the existing missions, contacts, etc. We've also been busily completing all incomplete content within the Paragon Wiki in case by some weird confluence of circumstance we are able to acquire the IP but not the code base so that we can implement the existing content if possible. The exact implementation details aren't set in stone though, so all of that is subject to change.
The main hurdle of reverse engineering is the client. If we go the reverse engineering route, we also almost certainly won't have the rights to distribute it, either. That means that you're on your own to get a copy of it, and doing so will be considered infringement around the same equivalent of downloading an old copy of some other game that's out of production. I doubt that NCsoft would pursue it, but it would make things harder in that we can't just put a link out there and tell people, "Run this to play."
I'm still hoping that all of this is moot. If someone else acquires the property, there won't be any need to distribute the server. Well, I take that back, sort of--I won't say no need, but we will choose not to distribute it because of the financial harm it could do to whomever purchased the property.
Regarding writing a new game: We neither need nor will seek NCsoft's permission to do this. While we might refer to it internally as a "spiritual successor to City of Heroes," we certainly won't be branding it as such. If we go this route, we will definitely need a lawyer to protect ourselves, but not to actually develop the game. That would come a lot later, once we get closer to release.
But having said all that...
I cannot emphasize this strongly enough. These options are down the road. We will not be releasing anything unless the official servers are turned off and we're convinced that there's no chance of them coming back on. If the game is acquired by someone else who runs it, we won't be doing either of these. It's a long time until November 30, a lot can happen before then, and I feel like working out the nitty gritty details of these options right now is jumping the gun. As severance agreements run out, I strongly suspect that we'll have a much better idea of where things stand.