anyone have any experience with failing sandisk cards?Yep, that happened to me with the 5D several years ago. Cause was definetive a defective CF card at the time.
On request SanDisk provided me with a free licence for a SW that recovers lost data from Flash. Not all data could be recoverd though. In fact the damage per picture was reduced, but most pictures had still some kind of damage similar to what you showed. In total the SW could save maybe 10% of the pictures, all other remained lost.
Guess this is why I like the two card feature that allows to write to two flash media parallel. Likelihood to loose data that way is much much lower, altough not impossible either.