Yes, it’s possible the lens was disturbed during reassembly, but it may not be permanently damaged. Removing the front element alone should not normally cause autofocus failure if everything went back exactly as it was. Common possibilities are: a spacer/washer was not replaced correctly, an internal part was loosened unintentionally, or more sand is still inside the lens.

If manual focus still works, that points more toward alignment/calibration or contamination than total failure. In many cases the remedy is professional cleaning, inspection, and recalibration rather than replacing the lens outright.

Best next step: stop opening it further unless you’re experienced with lens repair, and send it to Canon or a qualified repair technician. Be sure to tell them exactly what you removed and that sand was involved. A proper service would check for loose parts, internal debris, and optical alignment.