Gotcha. Gotta hate drunk vandals.
Replacing the housing is super easy. Like you said, pop the panel, unplug, remove the bolts, swap housings and reverse to install. Easily a less than 5 minute install.
I'm not sure on the part number.... The side mirror housing was the same for the 3 from '04-'09 both hatch and sedan, with the exception in difference between manual and power glass. You should be able to contact any Mazda dealer to get the p/n and price. You could also contact Jason at onlinemazdaparts.com (firstname.lastname@example.org) or another online dealer like mazdastuff.com. I'm assuming you're in Canada, but the p/n's should be the same for all of North America. The only difference would be the color of the front cover, and if your current one is still intact then you could order whatever color you'd like and swap them out.
As to heated mirrors if you're interested in them this would be the time to do them since you have the replace the housing anyway and heated isn't that much more. An OEM heated housing costs about $100. I think the non-heated is about $75. You could also go for an aftermarket housing if you'd like. HERE's
a site that sells some....... $64 without heaters, $90 with. Sad, they used to have the heated housings for $60.
Anyway if you did that you could still get just a heated glass portion for the passenger side and retrofit that one.... save you ~$50.