As the spring weakens, the brass will be tossed farther and farther until there's not enough strength to feed the next round.
If you are shooting S.D. +P RDS, this will happen sooner than if you're shooting minor power factor sub sonic competition loads.
Yes they can last a very long time. The pistol and the type of ammo your shooting most often and the round count will drive the life span.
The changing brass toss distance woth a given load is an indicator.