S!
That is what happens. rivets loosen, bolts shear or their holes wear, structure like spars and so forth get "tired" of the stress and generate cracks in them. The cracks and damage are more likely if the airframe is stressed a lot already and older if comparing toa totally new one. for example Bf109 had structure life calculated to about 400 hours if flown within limits. This of course did shorten due damage and strain.
I read about Finns losing 2 Bf109's to structural failure in combat. One was in a speed exceeding 900km/h when the wooden tail broke off and plane crashed to ground. Pilot was KIA. The other was a Bf109 losing it's wing in a tight turn due the bolt keeping wing attached failed and broke. Pilot KIA. There are some text about the plane surface buckling or similar after hard turns and older airframes feel "mushier" than new ones. So strain has degrading effect on the plane.
As said, implementing G-factor to IL-2 is very interesting thing
Waiting for it very much.