Workout not saved before battery ran out

I went on a 21km hike today, tracking it with the Workout app. Unfortunately, near the end of the hike, I got a battery warning and when I actually finished, and pressed save, the watch went into low power mode.

I put the watch on to charge and, a couple of hours later it was ready to use... but I now can't find the workout session.

Is it lost forever or is there some way I can get it back?

I can't find it in the workout app, and there is nothing in the Activity app on my iPhone.

Is there anything I can do to prevent this happening in future (besides saving workouts a lot earlier, even if they aren't finished)?