Yea that's what I thought. For this reason I keep a cold spare ready to go in case of a disk failure.
I honestly didn't even notice the data being missing as the array kept on trucking without a problem. I was surprised at how even though I had lost 2 disks all my data was seemingly present and available, the content I was missing was older and unused. Sadly I was mistaken at how UnRAID functioned, but now I know better.
A second parity disk may help in these cases of losing 2 disks before parity can be rebuilt, but a rigorous backup makes far more sense to spend time on.
Limetech supports BTsync in a docker container which could be used to replicate data from one UnRAID To another.
BitTorrent Sync