Saving MUDs?

chewedtoothpick asks: "My absolute favorite game of all-time, Exile [Archive.org mirror], is a MUD that is about to be shut down, and I've noticed that MUDs have been diminishing in number, especially lately. Why are they all quitting, and what does it take to resurrect them? Is it a matter of buying the code off the creator? Is it a matter of making your own and hope it comes close to the one you want it to be like? Is there nothing we can do to save the classics that define multi-player games?"