Bad disk removal on Raid 1 for EX2 NAS

If I need to remove disk 1 from my 2 disk Raid 1 EX2 NAS device for replacement, will the unit still be available to me until I get the replacement disk?

I believe the answer is “Yes”.

however. . . .NOW would be a GREAT time to do a backup of all the data on the NAS (by whatever means necessary)

Both disks are probably about the same age, correct?
When you put the new disk in; it will “mirror” the existing disk.
That would be a bad time for a drive problem to occur. The fact that the two disks are the same age . . .means both could be “ripe”.