Blocked path

Hi again.
Here is my problem:

The NPC is allready on the way along a path. Then the player builds an object that blocks that path.
When my NPC reach that object it can’t move further. It’s just standing there trying to walk through (if I remove the object, the NPC follows the path as planned).

Is there a way using A* to get a feedback when the NPC aren’t moving along the path/can’t reach the next point?

Created a solution using IsPathPossible (a,b) between current waypoint and the next before incrementing current waypoint. If the path is not clear, run another code that sends the NPC looking for another way.

This may not be the most effective way, but it works…anyone who has a smarter way?