1. Can I restore firmware without erasing the data on the disks?
Theoretically, yes, of course. In practice no, probably not. The 'emergency reflash' procedure (using an USB stick) reformats the disks. So to repair the firmware without erasing the data you'll have to do it manually, over a serial connection. Which is beyond your skills, I guess.
2. What is the easiest way to get to the data on the disks from a windows environment.
Not. The data is stored in an xfs filesystem, on a logical volume in a volume group, on a linux software raid array. All these layers are not supported by Windows. You'll need a Linux system.
(The data was protected using the local active directory).
Fortunately that is not important. The protection is enforced by the OS. The data itself is just plain data. If you have the rights to mount the disk, you also have right to read the data. (Unless encryption is used)