Any damage to Water heater when main water shut-off for a prolonged vacation in Texas
There should be no damage, but of course this would be non-freezing conditions. What setting would you leave the heater on? If electric, I would say switch off power to the heater. If gas, switch to vacation/pilot setting or even turn gas off at the heater.

Upon return I would turn the heater to hot (140 F) and let it come to temperature, then run hot through all delivery points.