Textured 3D was coming whether you liked it or not and 3DO/Saturn/Playstation all instantly aged the Jaguar/SNES/Megadrive over night. The 486 PC + byte per pixel VGA screen mode also did the same to the Atari and Commodore computers.
A chunky pixel mode on it's own wouldn't have made a huge difference, it would have needed a texture mapper added to the blitter as well.
If they could have achieved that around the a500+ timeframe then it could have saved them. The amiga had already started winding down by then and needed a shot in the arm. ECS was not good enough to keep people buying amigas. They could probably have stuck with a 68000 and still had some good games.