Through some lucky combination of reset button and unplugging-replugging the USB cable and quitting-restarting the IDE I was finally able to upload a different sketch and get the Micro to respond. Commenting out the sprintf in the original sketch and replacing it with a bunch of lines of print statements resulted in a working sketch.
I can't even begin to express how much I hate the absolutely primitive "print" command available on Arduino. Writing 4+ lines of code per line of output just to display the values of a couple of variables with labels indicating which is which is just nuts.
Thanks for the help. At least my Arduino Micro isn't ruined.