Damn it. Why did Honda stop building the Civics with folding mirrors? I notice the 98 Accord lacks folding mirrors, but they're back for 99. I guess a significant number of people complained about the lack of this essential feature.
I surprised by the number of people who can disassemble and rebuild a computer in their sleep and yet are scared of the simplest things on their cars.
Anyway, remove the triangular plastic piece that covers the inside of the door where the mirror attaches (use a small cloth covered screwdriver to carefully pry it off). You should see the screws that attach the base of the mirror to the car. Take that remaining part off the car and mix the epoxy. Glue them back together and let them set. Then reinstall in 24 hours. If it doesn't hold, try some different adhesives. This is really your only hope for not needing to buy a replacement. If it still doesn't hold, try junkyards (used parts) first, then call Napa (a long shot but some non OEM might make replacement mirrors for less) and then the dealership.
Good luck.
EDIT: Don't try to simply glue it back onto the car. It will never hold. Remove the remains of the mirror from the car (as if you were removing the entire mirror), repair it, and then reinstall the assembly after it has set for a good 24 hours.
