The firmware can be reflashed using a USB TTL programming dongle wired directly to the controller board. There are instructions out there. Of course that method isn't for everybody but the usb dongle costs almost nothing on ebay.
If you have a lot of S3's and plan on keeping them long term this is a good idea. But it does take a more technical user then one who gets new flashed board from Bitmain.
I will admit on the one S3 I bricked I just paid for a new one with good flash on it. They did a good job getting it to me pretty quick. Just was easiest option at the time for me.