You would store the X and Y at the time they decide where they are going to go in a instance variable on the object. Like when you mouse click somewhere, or if they are set to goto "the mine" or wherever.
Then after recalculating the path, you would use
Find Path To (previous destination)
to reroute them to the same location again.
I think that regenerate path keeps their previous destination in tact though when you run it. i could be wrong.