So you want to prevent the situation when turrets are completely blocking the path to the target, right? But if an enemy can walk around the turret - this is allowed?
Recalculating the pathfinding map and path is the only option here.
If pathfinding plugin is using too much cpu, make sure that the layout size is set correctly (not bigger than the level map), try changing pathfinding cell size.
You can use EasyStarJS instead of Pathfinding - it's massively faster, but only works with tilemaps. So you will need to make some changes to your game to accomodate it.