Hi Alfred,
No since a tool window's lifetime is not until you close it and remove it from the bar manager (it can still be available but not "active" in the layout). This is different from a document window's lifetime, which is intended to generally only be while it is displayed. We do have a property that controls whether document windows are disposed automatically but not tool windows, and that is because of the lifetime designs.
What you probably could do is handle WindowClosed and in that, remove the tool window from the DockManager and dispose it if you no longer need it.