This is both a visual and usability request. Having the presence of an Orion window be contingent on an open tab means that moving that tab to a different tab group closes the Orion window as a whole. I feel that the default state of Orion should be no open tabs at all, with a blank vertical tab list and an open search bar at the top. See the below screen recording for reference. When closing tabs generally, closing the last open tab shouldn't close the window as a whole (this would replicate the experience on Safari — see the second below screen recording — whereas the current experience is more similar to Chrome's). Just a note that the Orion window does not quit, it just closes but Orion remains open as an app.
Introduce a different default state that doesn't involve having an open tab.