We will find out next year in UK as the new Military Flying Training System (MFTS) kicks in - much of the training is synthetic (and not in FFS but part-task trainer type 'sims').
I don't think you can 'replace' any of the real aircraft training for many of the reasons articulated above - sim training is good for enhancing skills or consolidating drills and processes or giving the student an idea of what they will face in the airborne lesson.
I have yet to fly a sim that flys like the real aircraft - they are all (very advanced) computer games and relying too heavily on them (because they save money) will just reduce the overall quality of your training product for real world ops.