According to the bungie.net website, Myth II's servers are now operational.

MythII's servers are alive and well, and anyone who has an unmodified installation of version 1.3 or higher should be able to log on with no problems. If you have removed/modified certain files from your Myth II plugins and/or preferences, you might not be able to log on. While there are various fan sites posting their own patches to allow you to get onto bungie.net which you might be considering, please be advised that these are not official Bungie patches and may not work as expected! Use them with caution (if you must use them at all). We are working on a patch that will fix up anyone who is having difficulty connecting to bungie.net, and appreciate your patience.

Myth TFL's servers are apparently also up, but won't work for everyone until all internet systems become aware of the their domain name change. It's not yet clear how long this will take.