There cannot be contingency plans for every conceivable scenario.
But it would have been easy to send out an astronaut to check the tiles if there was a clue that they might have been damaged. If damage was found. Extend the stay in orbit by turning off systems, like Apollo 13. And send up a second shuttle to bring people home.
Don't tell me they couldn't have launched another shuttle in 2-3 weeks if lives depended on it.