The risk of multiple moon landings and takeoffs is really quite small as the moon has no atmosphere. Perhaps not mission critical small, it might be in the ran

The risk of multiple moon landings and takeoffs is really quite small as the moon has no atmosphere. Perhaps not mission critical small, it might be in the range of 0.1-2% risk for each landing/takeoff cycle. So if you require 10 refuelling launches, your total risk is 1-20%. Say you had a large moon lander, or multiple landers that make up a robotic fuel collection and refining system. Then you have a reusable lander-launcher that lands, collects the fuel and delivers whatever it doesn't use for takeoff/landing into a orbital fuel deport orbiting either the moon or earth. Actually might be best to have your deport orbiting the moon until it's full then send it on a slow, low-fuel, multi-month path back to earth orbit, perhaps you meet the Mars transfer vehicle there. If at any point the fuel transfer lander-launcher fails, you can launch a new one from earth and push back your Mars mission. Perhaps you have multiple fuel transfer landers as a contingency, or to increase throughput (fuel in orbit isn't just useful for a single Mars mission) Only once you have your fuel ready, do you launch your Mars crew. You could do a similar setup at Mars to collect fuel for your trip and avoid having to drag that fuel from the moon. But a Mars fuel transfer lander-launch would be much more complex and risky, and it would be a lot harder to land the fuel collection/refining facility.