This image, along with several others, was taken by the Air Force Research Lab's AMOS telescopes during several passes some 4 days before reentry. I've seen higher resolution versions of the images that show tremendous detail. Had someone thought to image the underside of Columbia, they might well have seen the tile damage.

Four days isn't a lot of time to do anything, but had they known, there may have been some things they could've done. For example, if they shut down the experiments and went to minimal power and activity, they might've been able to stretch their consumables by a few days. That might've given them some time to consider alternatives like some form of consumables resupply (unlikely), an alternative reentry profile, or a rescue mission. I don't know if any of those things would've worked, but had the proper images been taken, time would've at least given them time to try for options. They knew the foam had hit the underside of the wing, so I have no idea why they didn't image that side of the Shuttle. Perhaps they didn't want to disturb sensitive experiments or the crew's schedule. One can only wonder.