I'll back up what everyone else has said that nitro won't affect the life of the engine with the caveat that you use enough oil (and good oil) and that the % of nitro is suitable for the engine. You can run in an engine on whatever fuel you like and swap around between different fuels whenever you like and it won't do any harm so long as you retune to suit the new fuel.

Your 80/20 fuel is called FAI fuel but only because that's the mix required in a couple of competitions run under FAI rules. In America it's become common to call any fuel without nitro FAI to the point where some companies (Morgan for one) sell a fuel called FAI but it isn't. I haven't made up my mind whether they don't know what they're talking about or if it's just false advertising .

I've never yet come across an engine that doesn't start and run perfectly well on zero nitro so to me nitro is more of a fashion accessory unless you're in a competition where you need every bit of power possible. This applies to 2 strokes because I have zero experience with 4 strokes.