[Newworlds]

I would say 6 months or a year. Many MUDs on the list are years old without connection.

I'm not sure of your system or how hard it is to have the system check, but if it checked all the muds for successful connection once a day for 30 to 90 days that would be sufficient. Even if you limited the checks to once a week and mark a mud dead after say, 10 weeks of consecutive failed connection, mark them dead.

On the other hand, if at the same time, the system checked the listed MUD's main homepage and came up as a dead link you could mark it dead simply based on that. Anyone with an active mud would be quick to let you know or fix that dead link.