The button immediately to the left of the slice offset slider is the maximize/restore for the slice layout. This is a new button recently added. See the following for details on that feature
There isn’t a button for resetting default orientation. You can change orientation in the slice view pop up widget that displays when hovering over the slice offset slider area. There is a combobox for selecting orientation.
You can also set orientation programmatically like so:
orientation = slicer.app.layoutManager().sliceWidget("Red").sliceLogic().GetSliceNode().GetDefaultOrientation()
slicer.app.layoutManager().sliceWidget("Red").setSliceOrientation(orientation)