i would wash it -- i would also toss it into the dryer and dry it-
hanging king sized quilts when wet can cause the quilting threads to break from the weight-
it is recommended to either dry them in a dryer or lay them flat to dry- but from the sounds of it there really is no reason to not be able to wash and dry it.
you might want to use a low-heat setting on the dryer- i'm never that (cautious) with my quilts i wash and dry them all the time....i do take them out of the dryer- give them a shake and put them back about every 20 minutes otherwise they wrap all up and don't get dry.. but that is as special as i get. i also use a regular cycle- warm water and laundry detergent when i wash them- even the silk and wool quilts - i've never had anything bad happen from washing my quilts...and treating them as if they are any other bedding item i own.