If collins was let live at all the brits would be smart enough to realise he's auseful shitstirring machine and probably woulda been sent to ww1 in trench coat work on subterfuge side of stuff with a promise of post war amnesty, from which he would never return one way or another. I don't actually think he was a nazi.
I'd agree with you, not a Nazi - but you could see a path in the 1920s where had he lived he could have become a dictator, such as was fashionable at the time. (would collins have handed power over to FF in 1932 for example?)