I'm not sure how this ever happens, but I've occasionally heard of people having leftover pie. The question: can you freeze pie?
The answer: It depends on the pie. Cream based pies don't freeze well - they will likely separate when defrosted. But fruit, pumpkin, and nut pies usually freeze just fine. Freezing in slices isn't the best route to go though; you're better off to leave the pie whole or in as large a wedge as possible (the less filling exposed, the better). Wrap the pie in plastic wrap, then place in an airtight container or resealable bag and freeze for up to 6 weeks. Let the pie thaw in the fridge before serving.