This is me fully loaded on a trip from Helena, MT to Prescott, AZ using Giant Loop Coyote bag. With that set up I could technically be out for 3 days before stocking up on more water. You just have to pack like a backpacker and you will be fine. Also depends on how much you weigh. I'm 5'10 160lbs.
Sure it could do a 20,000 trip, but it needs to be a low mileage bike or one with a rebuilt engine. You start getting into high mileage and you start getting into a high possibility of pushing the 249ishcc engine too far. At 50,000 + miles my 2010 KLX decided that it was tired and had had enough. The KLX is a tough bike. It was the bike I learned on, held its own on the freeways and around cities and took everything I threw at on the back roads and trails in MT, WY, UT, NV, ID, AZ, and around New England.