If you're willing to believe that he showed up for duty in Alabama, yet no one there remembers this future president of the United States... ...then let's take a look at this excerpt from the Texas Military Code.:

As is evident from the above, one of the elements of desertion is intent to remain away permanently. Bush asked for discharge from the TANG on September 5, 1973, and apparently left for grad school immediately after. (Does anyone know of university grad school years starting after September?) Now, let's take another look at that excerpt from the Texas Military Code.

So... On September 5th, 1973, George Bush asked for discharge (resigned from) the Texas Air National Guard, thereby stating his intent to not return to duty with the TANG. Now let us examine another document

That document is Bush's Discharge from the TANG. Notice block 33, at the bottom: "NOT AVAILABLE FOR SIGNATURE". There it is, folks. Bush left Texas before his resignation from the TANG was approved. There is your evidence of desertion.

Thanks, Hank!