This is all very, very fascinating and quite nostalgic too for me personally.
The reason being all this talk of Big Chap surviving reminds me back in 1979 when my elder brother having seen the film, told a much younger me how the Alien was indestructible - that is, it didn't die at the end. Now of course we know (after many more films) that yes they can be killed but I like the idea of Big Chap, whilst toasted up, somehow surviving and then adapting to something more which would tie in nicely with Ash's perfect organism monologue about Structural perfection.