It looks like you already have an old work box, which is what you need if there is no stud. It's possible the wings just got pushed in and thats why it fell, or they ripped through the drywall because there is a chunk missing there. If you remove the fixture you should be able to see the screws to clamp it back and you can just rotate everything so the wings are secure behind undamaged drywall. (When you rotate the box you will have to adjust the fixture mount to keep it level)
EmpressH t1_j11vhor wrote
Reply to Vanity Light Falling Forward by miacane86
It looks like you already have an old work box, which is what you need if there is no stud. It's possible the wings just got pushed in and thats why it fell, or they ripped through the drywall because there is a chunk missing there. If you remove the fixture you should be able to see the screws to clamp it back and you can just rotate everything so the wings are secure behind undamaged drywall. (When you rotate the box you will have to adjust the fixture mount to keep it level)