Looking at 1985, the top 5 guys in complete games were Bert Blylevn (22 year career in MLB), Doc Gooden (16 years), John Tudor (11 years), Charlie Hough (knuckleballer so you can throw him out, 24 years), Mike Moore (19 years), Fernando Mania (17 years).
Looking at 1990, Ramon Martinez (13 year career), Jack Morris (18 years), Dave Stewart (16 years), Bruce Hurst (15 years), Doug Drabek (16 years).
As far as memory serves, none of those guys above had their career end due to injury. They just got old.
At least back then, there doesn't appear to be a correlation between # if innings pitched and injury.
One thing I'm not sure how to account for is today's reliance on velocity. I'm not sure other than Doc and Jack Morris and maybe Dave Stewart, any of those guys would compare to todays upper-90's max effort guys. It does seem like every pitcher today has a upper 90's fastball and a 90's hard slider. I don't think there's any doubt that today's harder throwers are more susceptible to injury.
But that goes back to having them learn to use multiple pitches through 6-7 innings, rather than just throw 99 for 4-5. The way we develop pitchers these days is almost like their disposable. Throw hard until your arm blows out, and we find another one.
Guys like Aaron Nola, Kershaw, Verlander who have a well developed arsenal of pitches don't have to throw 99 to be effective. But the guys who develop like that seem to take a backseat to guys who's only asset is velocity.
I'd love to see a graph of injury vs velocity - how many guys are more likely to get hurt living at 91 mph, 95mph, 99mph?
We all love Kopech right, but who didn't see that coming?