What if I have two simultaneous failures of different ASM Failure Groups?

This will usually force a dismount of the disk group. Any attempts to access the files in the Diskgroup will get I/O errors. If access to the Failure Groups can be restored with no data loss, then the Diskgroup can be mounted again without rebalancing. This happens if there is a failure of a piece of hardware used by multiple Failure Groups.

If two disks in different Failure Groups fail, but not the entire Failure Groups, then there is a reasonable chance that the two disks do not mirror any data, and the Diskgroup will tolerate the failure.