I want the elements in a swimlanes to persist when the swimlanes are deleted. It is annoying in our case for users to have to recreate all the elements when they just want to remove a swimlane.
Instead of outright deleting swimlanes, provide an option to archive them. When a user archives a swimlane, the elements within it are preserved but hidden from view. Users can then choose to unarchive the swimlane at a later time, bringing back the elements.