Last time I built a RAID 1 array (mirrored, you mean?), IIRC the BIOS gave the option to specify which of the disks was the one to duplicate.
So unless I'm missing something, you could proceed as follows:
Put the disks back in, and break the array. That should give you two disks, one of which is a bit more up to date than the other.
Decide which of your two disks is the master, and specify it as the source when you rebuild the array.
The BIOS should then just splat the contents of the source over the target (takes a while), and you should then be back in business.
Just make absolutely sure you know which is which - physically, and by reference in the BIOS. There's no recovery from picking the wrong one :)