When Challenger exploded, there were several issues:first, the flames coming from the SRB licked the ET located next to it and the ET explosion destroyed the orbiter also located next to the ET. We know the upper part of the orbiter was almost intact until impact on water.
Using a conventional rocket , a capsule (on its top) would have been protected from an explosion occuring underneath it, not just thanks to its heatshield but also thanks to the shockwave that would have pushed the capsule away from the flames. And, of course, a capsule must carry a parachute.
I'm sure that even without a LES, a capsule would have saved the crew (like it saved the Soyuz 18A crew that landed near the Chinese border when the last stage could not separate from the second stage a few minuted after liftoff). I'm sure the LES was already gone when the problem occured.

Raoul