Yeah, as long as you can trigger the fix by continuing a game with a character whose challenge progress calculates to more than your current BAR total**. You'll also get back any missing head/skin rewards (not those picked up, and not sure about the SHiFT Halloween ones).
If you have multiple characters, you'll need to continue a game with each of them (after triggering the fix) in order to restore their BAR and heads/skins.
GBX is urging people that lost more than 10 keys to file a ticket at support.gearboxsoftware.com
(after the update) to obtain the remainder.
** The fix won't trigger in certain situations, such as playing a new/multiple characters after the BAR reset and having since accumulated more BAR than any single character's challenge progress represents :(
...and lost stash items are gone for good.