What app are you using for Navigation? I'm using CoPilot Truck and am using Tasker to return to CoPilot if CoPilot is in use when I answer or ignore a call.
I'm sure the same is possible Google Maps, though it would prove a little more complicated to implement since I'm using notifications to determine if navigation is active, and Google Maps notifications are inconsistent during navigation.
Note that I'm also using the paid version of AutoNotification on KitKat, but it should still be manageable on without AutoNotification on earlier versions of Android.