[SamKeck]

Shortly after Columbia lifted off Jan. 16, a piece of insulating foam on its external fuel tank came off and was believed to have hit the left wing of the shuttle. Leroy Cain, the lead flight director in Mission Control, assured reporters Friday that engineers had concluded that any damage to the wing was considered minor and posed no safety hazard.

From an earlier article on Yahoo News.

[Zebra]

Question. What if the engineers had concluded after lift off that the damage was re-entry compromising? What would/could they do?

[Gracey]

.....a piece of insulating foam on its external fuel tank came off and was believed to have hit the left wing of the shuttle.

Thanks for this.... I'd say it caused some critical leading edge tiles to come lose and consequently, the space craft could not absorb the head and melted the aluminum body. From a timeframe that it occurred, it seems feasible. Thanks I worked on Shuttle Program for most of my career.