Would we all be wearing flares now if it wasn't for him? Probably not, although let's face it, some people still do.
Would The Sex Pistols have been anything other than a dream if it wasn't for him? Probably not, although I personally think that they still would have been The Sex Pistols that we all know and love - we just might never have heard of them.
Would the last quarter of the 20th century have been quite as much fun without him? Probably not, although I for one await John Lydon's thoughts on that subject with no little interest!
For what my opinion's worth, he might well have been the catalyst that sparked the revolution, although I'm not entirely sure that the revolution wouldn't have happened (or indeed was happening) anyway... but for doing whatever it was that he did and for doing it so well, we all should be grateful - not sure about the tartan suits though...