I would suggest that get at least one other opinion.
You didn't mention where your boat is, but I agree that most rigs don't need to be replaced after only 10 years.
It is often easier and faster to do a re-rig if you pull the stick. If there are other issues that need to be addressed it may make sense. If you are just replacing the standing rigging and the boat is in the water, it seems like overkill to me.
It would take two men about an hour to measure all the shrouds and stays with the mast up. Then he could fabricate everything in his shop and everything could be installed in about three hours.
You might want to ask the guy to elaborate a little more on why he feels the mast needs to come out.