your pico8 zip is in your PC right? if not
try to use winscp(use the cpi:cpi ssh account to login ) to copy the pico8 out of GS
but I remember that if you buy a pico8, you will have a download link in your email
so basicly , there is no need to worry about pico8,wont let you buy again
and the data in retroarch can be found and setup again because retroarch is opensource
here is the os image
use dd(linux) or win32 disk Win32 Disk Imager download | SourceForge.net
to do the it ,flash the image into a TF card ,8G space Minimum