It also depends on whether you sent it for a warranty repair (and when), because if you do, they'll flash it with the latest stable version of SailfishOS and it then becomes your reset point.

By the way, with the ssu release x.x.x.x && version --dup, can one safely downgrade SailfishOS as well?

The reason why I'm asking is that I need to send my Jolla for a warranty repair, but I'm worried that they'll flash it and I'll never be able to go back to Sailfish 1.0 (which I greatly prefer over v2.0). I naturally asked them about it, but they are not responding.