Sure, doctors have a social life, have children etc. It might be a challenge to go part time (as it is in many jobs), but plenty of people do it.
Bear in mind that just because the number of paid hours is going down, this doesn't mean there will be sufficient cover ('Hospital at Night' schemes for example) that doctors feel they can leave their patients and go home at 6pm or whatever. I get the impression from a number of junior doctors that the NHS is going to be replying on the good faith of doctors in staying longer as they're not going to be able to provide adequate care if every doctor just works 48 hours.