First and foremost this is NOT a historically accurate portrayal of the Pistols career. It was never meant to be.Everything, literally everything that happens in this movie is there only to provide context for the doomed love story of the two main characters.The number of inaccuracies run into dozens, from the portrayal of Rotten as uncultured buffoon (he was anything but) to the creation of "Rockhead" who as far as I am aware played absolutely no part in the proceedings as he didn't actually exist.The other Pistols were treated as bit part players in all respects (no-one even bothered to get anyone who looked or sounded like them)I did like David Haymans Malcolm McLaren though- well scripted, well played.The point of the movie is the all encompassing mutually destructive interdependancy- in all senses - of the two protagonists. Their descent into hell, against a backdrop of ridiculous fame and notoriety. Their eventual surrender to a drug which excludes and obliterates anything but slavish devotion to itself.
The movie certainly achieves its aim of portraying Sid and Nancy as hopelessly devoted to each other and the drugs.The focus shifts away from the disintegrating punk scene, via a stuttering attempt at a solo career towards a relentless personal battle that was only ever to have one outcome.Gary Oldman is really rather good at capturing some of the shambolic nihilism of Sid, whereas Chloe Webb makes Nancy a totally unsympathetic character it is so easy to despise.
Whether the final fight that ended in her death is anything like the movie portrayal we will never know. I'm guessing that the scene was fanciful at best and just completely invented at worst.What matters with this scene, as with the whole movie is that it is a take on what may have happened. It isn't supposed to be a documentary. It is pretty good for what it is.