"Odds are something greater than 0%.
Always, with any update like this...drive firmware, BIOS update, whatever...be prepared for massive fail."
I totally agree with USAFRet. If/when I update firmware for SSD's it's always with great trepidation. Usually only do it if there's something that critically needs to be addressed.
My experience with Intel SSD's and their updates has been flawless. I have, however, read mixed things when it comes to Sandisk and a few others. I do own a couple of Sandisks and have held off on updating them. If you do pursue this then follow the instructions they give exactly(still no guarantees) and as mentioned make sure you've backed up everything on the drive.