Maybe we know what would happen. It looks like they realized during the launch that there was enough damage done to the shuttle that it might not survive re-entry. I don’t know what they thought the odds were, or what they told the people on the shuttle (or who among them was told), but I think they would probably just go through the mission as scheduled and hope nothing goes wrong.
News reports that I read stated that NASA engineers didn’t notice the debris hitting the wing on liftoff until they reviewed the film of the liftoff, many hours after the liftoff occured. By then, the shuttle was already in orbit or very far along the way to reaching orbit.
In any case, way too late for a pre-orbit abort or RTLS.