The server technically still exists, but they permanently locked it down a few months ago due to drama. (I don't really know the details so I won't try to explain it)
Definitely a shame considering the modding stuff is effectively inaccessible now.
Viewing post in Toontown: The Grindworks comments
There is an unofficial grindworks server that basically serves the same function as the old one, and has all the same modding stuff. https://discord.gg/4RhfaHcJn