As Hunter already explained - it was just a "temporary solution" due to increased complains regarding bugs in the Mini World changes, and at the present Sane Mage is not active in the game.
I will be just adding CipSoft announcement - with exact dates relating to Sane Mage.
The official announcement of implementing Sane Mage was on October 15 2013 (removed on August 12 2014- so it was beautiful 11 months of holidays;)- https://www.tibia.com/news/?subtopic=newsarchive&id=2570&fbegind=30&fbeginm=7&fbeginy=2013&fendd=29&fendm=11&fendy=2013&flist=11111111
"Sometimes, even the maddest of mages needs a break to fight off the sanity that slowly creeps back into his mind. From today's server save on and until further notice, the mad mage is on vacation and does some soul-searching at the beach near his tower."
If you check the update thread when the Mini world changes were added July 06 2011- https://www.tibia.com/forum/?action=thread&threadid=3434041 - they were filled with many bugs. They have been reworked a lot and this was causing further- new bugs.
Then Masters Voice World Change was revamped on Sept 13 2013 (Major Update 10.02)1 and on October 09 20132- this has increased number of bugs for this particular Miniworld change (loot issue etc). Kindly see at the thread there and Mirade stating3:
"Due to the adjustments that were made with the second part of the summer update, and also last week, the world change has become quite complex scripting-wise. Adding the rules to adjust the world change according to the feedback have made it quite complicated, and also error-prone. It is difficult and extremely time-consuming to maintain and test the world change due to all the possible side-effects, dependencies and conditions that might interfere.
After a careful review, we decided that the best approach is to script the whole quest anew to include the adjustments properly and right from the start instead of spending time with making quick fixes that only complicate the script even more. A proper re-scripting is a project that requires some time (both from content team as well as the test team), though, and cannot be squeezed in between the current winter update tasks and projects. Therefore, we decided to close the world change for some weeks until we find time to do this properly. We will do our best to re-open it as quickly as possible but it may take a while."
If you wish and you are more interesting, you can also find the following document from the contest when the Mad Mage was "missing"- https://tibia.fandom.com/wiki/Scientific_Contest_(Book)
Officaly Master's of Voice returned on August 12 20144.
Also, the world change "Their Master's Voice" is now accessible again.
And even after this there was also another fix on 26th of August 2014. (most probably more after words).
So... it was a long ride of fixing.
1. https://www.tibia.com/news/?subtopic=newsarchive&id=2532
2.https://www.tibia.com/news/?subtopic=newsarchive&id=2565&fbegind=30&fbeginm=7&fbeginy=2013&fendd=29&fendm=11&fendy=2013&flist=11111111
3. https://www.tibia.com/forum/?action=thread&postid=35529957#post35529957
4. https://www.tibia.com/news/?subtopic=newsarchive&id=2852&fbegind=30&fbeginm=7&fbeginy=2014&fendd=29&fendm=8&fendy=2015&flist=11111111
5. https://www.tibia.com/news/?subtopic=newsarchive&id=2869&fbegind=30&fbeginm=7&fbeginy=2014&fendd=29&fendm=8&fendy=2015&flist=11111111