The tires will only last till they wear out................ :lol:
Kidding aside, a lot depends on you riding Habits, your Speed, the Weight you carry ect., so really the best your going to get is a guess , my guess (and hope) is at least 10000 miles--how long is up to you.
As far as storage, I don't think it would make any difference if the tire is off the ground since the bike is on the center stand there is very little weight on the rubber anyway. <s>