Microwave Crashing Down

If I were you I would call Fleetwood and get there advice. I've had to re-attach the front tv cabinet to the ceiling several times with screws and each time it failed and a cabinet to the sidewall and each time they failed. Then I got smart and talked to a Fleetwood tech, always use rivets into the ceiling and sidewalls. Still up there after a couple of years. I forget the name of the type I used but they star out when compressed.
Yours looks like some water damage weakened it and finally came down.
I would re-attach that angle iron with about 5 star rivets and I bet it lasts you.