Will this see the end of the Class 360s in west London?
That's the plan yes. They may hang on as strategic reserve but given the condition they are in and the rate of knots at which assurance documents seem to be falling into place for the 345's, I fully expect TfL Rail West to have an exclusively FLU 345 fleet for that timetable.
EDIT: I accidentally deleted the post that spsmiler is referring to. It's below on another thread added here for context.