I know how awful it is to have a cat missing in these circumstances, and my heart goes out to you and your family.
It may be worth a call to the local Council to ask if they're aware of any road traffic casualties where they've collected a cat from the roadside (I'm so sorry, but at least you would know one way or another)
Is Khan microchipped? You could also try contacting the main missing pet bureauxs as wellhttp://www.petsbureau.co.uk/lost_pet_services.htmlhttp://www.nationalpetregister.org/
It might also be worth approaching your local newspaper to insert an advert, or if your local television station would run something of an Appeal - given that Khan is a pedigree they may be able to run the story of him being AWOL alongside a public interest message? Also might be worth contacting local boarding catteries, just in case anyone sights him.
I hope and pray that you'll have news of Khan and, better yet, be reunited.