War Horse died, possible to get it back?

Solution 1:

Unfortunately, you cannot get it back. Once a horse dies, it stays dead permanently.

This has been confirmed by several external resources, such as:

• https://guides.gamepressure.com/red-dead-redemption-2/guide.asp?ID=46968
• https://www.businessinsider.nl/red-dead-redemption-2-players-keep-killing-their-horses-2018-10
• https://gamerant.com/red-dead-redemption-2-horse-dead/

As described in the first link:

The situations described above can lead to one of the two results:

• Your horse is gravely injured. You can still safe (sic) the animal if you have the item described below.

• Your horse has died. You can't bring the animal back to life.

Solution 2:

When it comes to the War Horse, Dappled Black Thoroughbred and Black Chestnut Thoroughbred, the "Special Edition Red Dead Redemption 2 Official Strategy Guide" says:

Note that horses exclusive to the pre-order, Special and Ultimate editions of the game are unique in that they respawn at the Valentine stable when they die.