I found that this is a fairly common problem with this mic.
I found a lot of people asking the same question.
I found a source for a replacement grill/sleeve assembly for roughly half the cost of a new mic.
What I did not find is a solution to the problem. Most responses indicated that it was not possible to put the grill back in place. Many had tried and failed.
So, I thought I'd give it a try and see if I could fail too.
Step 1: The Problem
Step 2: The Right Tool for the Job
Life will be easier if you also have something to use as a press. I used a bar clamp.
You may find that you'll require a small punch. I didn't have one at hand, so I abused a #1 Robertson screwdriver.
You will also need some epoxy cement. I used 5 minute epoxy.
Step 3: Disassembly
Unscrew and remove the collar from the body of the microphone.
Step 4: The Big Squeeze
There is a ring of dark, hard material around the bottom of the grill. I'm not sure what this but it will buckle and crack as you squeeze the bottom of the grill.
Position the edge of the clamp about 3/16 inch from the bottom of the grill. Any higher, and the grill will flare out at the bottom, which is counterproductive. Any lower and there is not enough of the grill exposed to catch the inside of the aluminum sleeve.
Tighten the hose clamp until you can feel firm resistance. Test fit to see if you can insert the grill into the sleeve. It will be a tight fit, and you will need to pry the grill into place. Insert the grill in at the spot nearest the screw on the clamp first, then work your way around.
If it won't go, tighten the clamp a bit more and try again. It may be possible to just tighten the clamp until the grill is compressed enough to slip in easily. I didn't try this for fear of permanently deforming the grill.
When you have the grill mostly inserted, move on to the next step.
Step 5: Another Squeeze
When the entire bottom edge of the grill is inside the sleeve, loosen off the hose clamp, and tighten the clamp/press until the grill bottoms out in the aluminum sleeve. Now you can loosen off the clam/press. The grill is a pretty tight fit. At least, it was in my case. I wasn't too worried about it slipping out again.
Step 6: Make It Permanent
Set the reassembled assembly upright, and lay a small bead of epoxy around the top edge of the aluminum sleeve, allowing some to ooze down into the gaps at the lower edge of the grill.
Place the assembly upright where it will not get knocked over. Allow the epoxy to cure until it is not the least bit tacky. Then let it cure a little more. You don't want to get sticky epoxy on the inner foam windscreen.
Step 7: We Are All Assembled Here...
Thread the repaired grill/sleeve assembly onto the body of the mic.
Set the mic aside to allow the epoxy to completely cure for whatever time period the epoxy instructions say.
Put the mic back into service.
Step 8: Done!
We'll see what happens next time the mic takes a nose dive.