I do not have specific Windows 10 knowledge (but have been using Software RAID arrays for a long, long time).
You definitely should not be trying to WRITING data to a disk on the array when it is not mounted - it can't end well. The data certainly won't be RAIDED when the system is restored, and will cause inconsistencies and possibly corruption.
Ignoring advanced filesystems like ZFS and BTRFS, filesystems expect to be consistent when written - and yours won't be.
Part of the problem is that the RAID array will not know what blocks have been changed - in case of where the file goes this will mean it won't be mirrored, but what would concern me more would be the divergence of information on the file allocation table or equivalent - ie the record which points to where files are.
As a best case scenario, if I were desperate (and I don't recommend you do this without a backup), I'd copy the file onto 1 disk, boot the system with only 1 disk, mark the array as bad and then rebuild it.