It is our duty as Christians to give them the message of salvation. If they won't hear it, kick the dust off of your feet as you leave.
It has been my observation that rarely does a non-believer "hear" the message the first time it is given. If we think we can just go around smugly reciting the "Good News" with a good-ridance attitude to those who reject it.... then we will saddly miss so many chances to eventually change lives. Rather we must be patient, live the example, plant seeds, cultivate the hope, give people a reason to want to hear the message, over and over again, building "precept upon precept" as the word says, never giving up hope.
I thank God everyday that years ago my friends did not "kick the dust off" their own feet and desert me the first time I seemed to not hear.