Very sorry for your situation. I have worried the same few weeks back as you are in today. Fortunatly my son got into UT CS.
If your son already had A&M admission, I will not worry anything but wait for the rest application results. Since my son did not apply for A&M and also passed the deadline when we started to worry. To avoid higher out of state tuition, the avaiable good option for your son now is to apply wisconsin madison CS program - it is relative cheap and easy to get into a good CS program. Deadline is Feb 1. You can rush SAT score if necessary.
Otherwise UTD deadline is 5/1/2022, you can apply after all options exhausted.
One more thing, you can also file UT appeal and attempt to get into engineering school or natual science Math program.
Good luck!