I doubt the .50 Barrett is going anywhere. The new rifle sounds like it’s intended for an anti personnel role and will possibly replace .338 LM rifles.
The .50 BMG rifles are used for anti materiel...sometimes including helmets, backpacks, and uniforms worn by the enemy.
I don't see the .50BMG rifles going anywhere. At worst, they'll be in inventory until the next big conflict, then every unit will fight over them until attrition without replacement wears them out.
The Barrett 50s will be around as long as they are serviceable and there is ammo in the stockpiles. It’s going to be like the B52...hanging around forever.