There will always be jobs for people who know how to fix mechanical stuff.
Like fighter jets.
Like fighter jets
You don't get it.
First off, there may be no fighter jets, just disposable pilotless fighter missiles. Such a weapon would be vastly simpler to build because there would be no need to provide for life support of a living pilot.
They would be simple and modular, and if they ever need "repair" it would be simply a matter of swapping a modular part, like replacing the battery on your cordless drill.
Or maybe a new part is printed on the spot, and the "mechanic" snaps it into place.
Or maybe they just print a whole new missile.
Or maybe damaged fighter missles are simply broken up and the resultant scrap melted or shredded and reused.
But there may not even be those: you're supposing the wars of the future will be fought like the wars of the past.
Wars may not even be fought against nation states.
Or wars may be fought by tiny insect sized weapons that swarm an enemy and sting the enemy to death if the enemy is human, or if machine, interest themselves into the gearing, vents, or circuitry to short it out or cut the connections.