I think the confusion here is about the marker type. My response was based on an Acquiring marker, from a unit firing at the moving tank. If that's the case, my answer stands. (Apologies, I'm very tired.)
If you are talking about the moving tank that itself has fired after assault move, then yes. But wouldn't you want to stay and finish the job on the target? It's a tactical choice and depends on the circumstances, of course. But if you choose continuous movement, yes, the Acquired marker would be moot. However, in Falklands and Heroes Against the Red Star, with Modern Vehicle AM you could fire first and then move, so you would want to keep the Acquired marker.