If both Arthur and the horse dies..?

[nyeglass]

If both Arthur and the horse dies by law/bounty hunters. Is the horse then dead forever and the horse that spawns with Arthur is the "new" horse or can you ride back and revive the horse with horse reviver? 

Good to know so I know if i should manually save the gave all the time.

[Kean_1]

I would manually save regardless at certain points but yeah, good question.  Never had that happen to me bu then again, I only lost a horse once so far and that was my own fault (I didn't beat the train). 

[Jackthestripper]

My horse and I were deep-sixed  by bounty hunters during one of the missions. When I revived, they gave me a different horse but I just went to the stable and picked up the horse I was using during that mission before I died. Of course I had to do the bonding thing all over again. If you return to the  area where your horse was killed, I don't believe it would still be there. And like @Kean_1 said, manual saves are important throughout the whole game. Hope this helps you.