Should be fine since it's not used by Unraid.
Disks 1 and 2 content might be OK but best to rebuild them in case it's not, so you just need to re-enable disk3, this will only work if parity is still valid, and it should be:
-Tools -> New Config -> Retain current configuration: All -> Apply
-Check all assignments and assign any missing disk(s) if needed
-IMPORTANT - Check both "parity is already valid" and "maintenance mode" and start the array (note that the GUI will still show that data on parity disk(s) will be overwritten, this is normal as it doesn't account for the checkbox, but it won't be as long as it's checked)
-Stop array
-Unassign disks 1 and 2
-Start array (in normal mode now), ideally the emulated disks will now mount and contents look correct, if they don't you should run a filesystem check on the emulated disk(s)
-If the emulated disks mount and contents look correct stop the array
-Re-assign disks 1 and 2 and start array to begin the rebuild.