There is evidence cocoons will survive prolonged freezing temperatures. A pdf search for vermiculture in Nova Scotia will find it.

i tried leaving a bunch of worms in a ground level bin a couple of years ago. no joy. worms may be ok with your ? -15? our -30 -40 was a bit much for them

here 'the Nova Scotia Agricultural College (NSAC) have confirmed that their cocoons survive extended periods of deep freezing...'

http://www.journalcra.com/sites/default/files/Download_206.pdf

checkout the photos from Sierra Worm Solutions of their outdoor in ground bins covered with snow. Scroll down to the bottom of the page.

http://www.sierrawormsolutions.com/wearegrowing.html

Worms can survive just fine, as long as you heat. I use rope light (as bottom heat in an enclosed space).

I left my compost bin on my front porch over winter, I am wondering if they will still be alive.

It depends on how much material you had in your bin and how moist it was. Even if your bin contents froze, some worms may be able to survive in air pockets. Cocoons will definitely survive and hatch once temps are warm enough.

Cheers,
Andrew