How realistic was the idea of sending another shuttle up to rescue them? Would they have had enough oxygen?

If they did a spacewalk and found the damage, what were their options?

They did a bunch of studies. While it was POSSIBLE to get a rescue shuttle up to them if they ignored a bunch of safety and refurbishment procedures, the sheer amount of complexities probably meant they would lose 2 shuttles and 2 crew.

> There was actually an exercise done to work this out, at the direction of the Columbia Accident Investigation Board (CAIB). [...] In the CAIB’s scenario, Atlantis would have launched with a four-person crew: two pilots, and two EVA mission specialists. [...]

> A Columbia rescue mission would have been the most monumentally difficult and epic space mission in history, and it would have required absolutely everything going right to bring the crew home safely. But NASA has shown time and again its ability to rise to the occasion and bring its formidable engineering and piloting expertise to bear. Instead, the worst instincts of the agency - to micromanage and engage in wishful thinking instead of clear-eyed analysis - doomed the crew.

https://www.quora.com/If-NASA-had-known-ahead-of-time-Columb...

A much more deeply researched article here:

https://arstechnica.com/science/2016/02/the-audacious-rescue...

The problem with sending up another shuttle is they hadn't actually fixed the underlying foam problem. If there was another foam strike on the rescue shuttle, now they have two craft in orbit with crew on that can't re-enter

One option would have been to place whatever high melting point metal tools they could spare into the hole, and freeze water around them to hold it in place. It also might have been possible to change the series of s-curves and other maneuvers done during re-entry, in order to lessen the heating on the left wing.