From the time that TinyTIM switched to MUSH-based code, the maintaining of the codebase was taken over by the Wizard/Administrator R'nice, who kept the program closed-source and made incremental and large-scale improvements to it for the next decade and beyond.
TinyTIM's co-founding wizard, Trout.Complex, has been a wizard on the same game for over 15 years without a break or sabbatical.