I think if you choose the option to kill 5 people 100 years from now, that 5 should not be part of your total kill count, because those people won't be dead for 100 years. In fact, it is possible you could commission a brick wall to be built somehow in front of the portal opening at the other end to divert the trolley in time, sparing those people, since the future (in my opinion) is not certain.