The Copper Will last forever, IF its not been opened ... when the air gets to it, is when it starts to deteriorate ...The jacketing on the cables won't last forever. Copper doesn't get along well with humans -- especially when it gets into the ground water.
When I open the lead from 1927 ... Yes theres still plenty of it out there in my city, its brand new ...
And thats the companies response as well ... look, its great, what have you repairmen been doing all along to ruin our lines ?
Well, once you need to open it to fix issues is when it start to go to hell.