The Wall of Khan bonus will always pay out if you have earned a spot on the wall, even if you leave or lose connection.
If you don't see the bonus immediately, please wait a few minutes due to the time it may take to fill up the Wall and calculate the bonuses for all the other players. If you close and then relaunch the app you should see a special message with your total winning chips within fifteen minutes.
You can also keep spinning and if you complete another bonus round, your Wall of Khan wins will be automatically applied to your total winnings in your most recent completed bonus.