I'm not sure if you played T3 or not, but no way in hell you should convert back to T3. T3 was unplayable, huge crashes, bugs and many other things that make it even annoying and unplayable. I understand that T4 is in a bad state and the activity is pretty bad there but that doesn't mean you go and switch to an outdated project that died 5 years ago instead of a project that is being updated constantly don't you?
To me, the problem here is, many regular/veterans left the server and players kept leaving (probably bored or left for their own reasons). T4 isn't a popular project and so is IVMP T3, T3 is dead, there is only one server that never ever reached 1 player base in T3(check game state). T4 is a new project that is not known, more advertising might solve the problem. Do not switch to a boring game mode, enjoy playing the current playable game mode. Again, T3 WILL NOT SOLVE THE PROBLEM, it will make players leave.