On Friday Microsoft released an update for Skype for Mac, version 7.8.390, that fixes the audio selection bug introduced earlier this week. In the new version Skype will again honor the audio device selections chosen in Skype > Preferences > Audio/Video. The prior version ignored these selections and defaulted everything to whatever was chosen in OS X's system preferences.
Skype for Mac 7.8.390 is available using Skype for Mac's built-in update function or as a manual download from Skype. Kudos to the Skype team for engineering a quick fix!