With the information comming from the wiki itself there is no rewards to keeping him alive. However you can kepe him alive through all those mutants (in what I assume is the following segment, I have not played the game myself)

In the Vault Dweller's memoirs, it is disclosed that Dogmeat died in the Mariposa Military Base after running into a force field (although in the game, it is possible to survive the military base with Dogmeat alive - usually by sealing him inside different rooms to protect him from the super mutants).

With the information coming from the wiki itself, there are no rewards for keeping him alive. However, you can keep him alive through all those mutants (in what I assume is the following segment, I have not played the game myself):

In the Vault Dweller's memoirs, it is disclosed that Dogmeat died in the Mariposa Military Base after running into a force field (although in the game, it is possible to survive the military base with Dogmeat alive - usually by sealing him inside different rooms to protect him from the super mutants).