If you didn't ever delete your Photosynth app between the time that you captured your panoramas and when you got home from vacation, I'm sorry. I don't know what went wrong and have never experienced anything like that with my Samsung WinPhone.
If you didn't delete your Photosynth app (and thus have a reason to believe that your panoramas' cube maps should still be on your phone, even if the app can't see them) you might be able to find some unofficial file explorer for your Windows Phone such as TouchXperience ( http://www.touchxperience.com/applications/summary/22/33.html ).
I've never used one myself yet and they most definitely aren't supported by Microsoft, so proceed at your own caution. If TouchXperience doesn't work for you, I don't really know of other Windows Phone 7 file explorers, so you should reach out to someone knowledgeable like Rafael Rivera.
The lesson for anyone is: Upload your panoramas to your Photosynth.net account right away + avoid this!