In the 1994 (red sky) season finale, Shredder and krang opened a portal to Dimension X, kidnapped an alien and mutated him and would turn him back if he lured the Turtles to the Technodrome. When the Turtles defeated some Rock Warriors and saved a village, the alien changed his mind and saved them from Shredder's retromutagen cannon, then they went for a ride in the Technodrome, destroyed its main engine, and allowed it to be pulled into a pit where it was fatally damaged. Shredder and Krang returned for a three parter in the last season as supporting characters and were sent back to Dimension X. In "Divide and Conquer", the series finale, Don and Mike went to the Technodrome to retrieve Krang's body with the size expander to help against Mega Dregg. Then when the body finally shrank, the Turtles pushed it and Dreg through the portal which finally destroyed the Technodrome and the current inhabitants. Who knows what happened to Shredder and Krang since the three parter (rhetorical question)?
--Previous Message-- : In the last episode, the TMNT defeated : Dregg and sent Shredder and Krang : back to Dimension X. And, since : the Technodrome was destroyed, it : seemed like they were stuck : there... :