Edit: The statement "Once they don't need them anymore, they'll be sold or scrapped" reminds me of a sea story.
Once upon a time, I was a lowly Lieutenant working in the Office of Naval Intelligence. We got hauled over to the Pentagon one morning because a topic pertaining to Iranian small boats (my area of expertise at the time) was a topic for the CNO's morning brief. We completed the briefing, and the CNO asked me how long these boats could be expected to run for while in an engagement with our forces. Without thinking, I glibly answered "Unless we shoot them, there's no reason to think that they can't keep running with us until they run out of gas, sir". There was a brief pause in the room while the CNO looked me in the eye and said "I understand that, LT, I was hoping you could tell me how long it would be before that happened". I had to sheepishly explain to him that was something that I didn't know at the moment and would have to go back and take an action to see if we had that data anywhere.
Both "They'll go until they run out of gas", and "Once they don't need them anymore, they'll be sold or scrapped.", are absolutely true on an infinite timescale, but bring little predictive value to the situation.