Same problem now, although it's editing a simple extrude feature that has a mirror as a child in a normal solid.
Having a mirror as a child means it won't let me add/delete refs but I can't quit anything with the 'outdated references' box open.
You should be able to cancel the Sketch tab to get out of it. It works for me in 4.0 M130.
You can then try edit references to replace the failed reference. You may have to replace the mirror feature.
I've just built a test model to try this again this morning & I can close the sketcher with the big red X in the ribbon on that model.
I was working on a production model when I saw this issue yesterday, I'm convinced it wouldn't let me quit but I don't have the model in that state anymore to verify that. The references dialog box does appear on top of the green tick/red X though so maybe I tried everything in sight other than that!, now I'm doubting myself!
Yesterday I ended up using resorting to File > Exit so I got the save ribbon thing at the top & managed to save all of the other models in session and only lose the one I was working on