It would be great if there was an option to have text at the end of a rall directive line. E.g. : rall-----slow. And for the money, to be able to have ending glyphs such as an arrow.
Would the “slow” be an indication of the new tempo?
Not really. in the current piece, the tempo reverts to what was previously current. I suppose we should make that explicit with a tempo indication. Good point.
I would use “a tempo” if that is what you are asking. Otherwise, it will continue on at the final tempo of the rallentando as would a live player who is sight reading until they realize that you could not have possibly intended it to be that slow. Dorico playback, however, is perfectly fine with playing the remainder of your work very slowly. 
Takes me a while to wake up. Of course it’s ‘a tempo’.
Thanks! I’d be lost without this forum.