First response from bds pretty much nails it.
I will only add that there are some folks who have some of the oldest imported Glocks who have reported that the polymer around the magazine well has cracked, yet the pistols remain serviceable. Glock would most likely replace those frames, as they seem to be very interested in the scientific/research value of such things. Of course those guns are now 30 years old, and three decades of use/abuse can send any pistol to the grave.
As mentioned, the G26 is not weaker in any way when compared to the Glock 19. While the slide mass is less than its bigger brothers, Glock addressed this by using a dual-captive recoil spring assembly. The larger Glocks, by comparison, use a single recoil spring setup. Likewise when you look at the longslide Glock 34, the folks at Glock removed mass from the slide to allow the same reliable function as the G17 while using the same loads and recoil spring setup.
I don't think it's reasonable to tout them as having an infinite lifespan, but we have to take note that the G26 was one of the very first production level sub-compact 9mms to be widely successful in the marketplace. Considering its popularity with LE and CCW holders since their inception, they are certainly tested and proven. They remain as the benchmark by which littler 9mms are measured, and rightfully so. The reason we don't hear about Glock 26s shooting themselves to pieces is not the result of people not shooting them; quite the contrary. It's because it isn't an issue.