It doesn't matter how fit you are, death will get us all the end. We live in hope all the time.
As for the last horse, he was the fittest but the inevitable was going to happen and the horse looked back to "home", happy memories before it was going to drown.
The hope could also be the owner hoping their horse survived.
And as for the song itself, it's very sad.
To me, the song meaning is:
It doesn't matter how fit you are, death will get us all the end. We live in hope all the time.
As for the last horse, he was the fittest but the inevitable was going to happen and the horse looked back to "home", happy memories before it was going to drown.
The hope could also be the owner hoping their horse survived.