I have had Ultrons. Skopars, Heliars since they were "day 1". I had a snapped aperture ring on a vII Color Skopar (fixed under warranty). The oldest ones I have are Snap_Shot Skopar, 50f1.5 Nokton, 75f2,5 Heliar - all going on 10 years now. All are used frequently (and not babied).
I suspect they will last as long as the current Leica offerings. Modern lenses are usually alloy barrels, plastic aperture blade 'drives" etc and you have to do the occasional tightening of screws or locking rings on all of them (Leica,VC, Zeiss)
On my later Summicrons (90's versions) I have had to replace aperture rings on some and also I had to have an Asph 35f2 redone as the aperture ring froze at 5,6.
The later Voigtlander lenses (28f3.5, Heliar 50 f2 and 3.5, Nokton 35f1.4 and Nokton 40f1.4 have held up very well in my hands - heavier build, some have brass barrels).
The early black Heliar/Nokton/Ultron used to chip the black finish quickly - no effect on function, strictly cosmetics.
Unless you are setting out to shoot 10-15 rolls/day, year in -year out - I would not worry. Either Leica, Zeiss or VC will last a long time.
On the Forum's you really only hear about the problems with lenses - not the majority of users who keep using them without any problems.