Is it possible for a night guard to serve as a temporary retainer?

Yes: If it was custom made and fitted by your dentist, and it is solid enough, then it can serve as a temporary retainer. If, soft and not well-fitting, then no, it will allow movement.

Yes!: If it was fitted by a dentist or orthodontist. The impression was made of your teeth in their current state. The fit of the night guard will perserve the alignment.

Yes and no: Depend o the type of the guard. Is it soft or hard retainer. Consult your dentist.

Yes: Clear night guard are passive they are thicker. They can be used as temporary retainer as long as they fit well and tight.

Purpose: Just remember the purpose of a night guard is to protect your teeth from bruxsim, clenching, grinding, --- the heavy load that you put when you're stressed or during sleep when you're not "in control" if you will, and a retainer is to help maintain the position of teeth.