Not if you use raidz1, if you use raidz2 then yes. raidz in zfs is pretty decent. I have had a disk fail in raidz1 and replaced it with another and no data was lost after a resilver. Took a few hours but worked really well. Pretty much the whole idea of using zfs is the enhanced security of your data, seems strange to not put that to good use. The chances of BOTH drives failing before you can replace 1 are very very slim. I get that there is no easy way to just migrate to raidz1 but you could if you got 3 drives, make a new raidz1 pool, copy the data across and then add the old 2 drives to to the pool with a new vdev. You need to be able to add 5 drives to the system though. Of course there are many options here, but you already know that