Yes, indeed, we recommend complete removal prior to a re-application.
I had Veil G2 on my vehicle for 5+ years before having to replace my headlights due to the need to replace a headlight housing (veil was still going strong).
We would expect G4 to perform similarly.
Depending on environmental conditions, yes you would likely see the film deteriorate or look worn (due to stone chips, etc) before deciding to re-coat.
Obviously, your circumstances may vary, but you have the idea...