Maybe the gate at yellow doesn't open until everything on Level 4 of Talushorn is dead?
I just checked with my saved game, all the Taurax are dead.
All things considered, I thought that was the "point of no return".
It seems odd that the entrance to the *boss room* was made to open with version 1.04 when General Ghorr dies, but the gate blocking your exit to level three remains closed.
The point of no return should be the Crux chamber. When you step inside the Crux chamber, a couple of tiles check to see if you have the Strange Viewing Glass in your possession. If you do, you are sealed in the Crux chamber. If you don't, you can leave the Crux chamber. I think this check should be extended to include the Crux of Fire. You should also not be allowed to summon Korren into the Crux chamber without having the Crux of Fire in your possession.- - - - - - - -Frivolous Mode Activated!
If you ignore/fail the puzzle on level three of Talushorn you can now open the gate to go back to level two if you use the wooden lever at the back. What bothers me is that only the middle section opens up, why are the other two tiles ignored? All three should rise!