Hi @snowbird12
Your already published menus will not be erased, so they continue working unless you manually remove their shortcode.
Although on this page I think you’re using their widgets and not their shortcode, which means that Gutenberg will have absolutely no affect on their display. Gutenberg is a post/page editor, but the widgets are displayed by the theme and managed at the Appearance > Widgets.
So the answer is the same as for the shorcodes: unless your remove the menu’s widgets, they’ll continue to work.