firmware OS of the snes cartridge is saved in flash nor memory ST M29W640FT
Given the Jedec standard of minimum 1 year power-off data retention is pretty much the worst-case scenario of after the maximum rated 100,000 writes (per
the datasheet) and 1-year power-off at 85deg C, you'll pretty much want to do the opposite. Presumably the chip has only ever been flashed once (which is good) so it makes sense to either store it at the minimum rated storage temperature of -65deg C or to keep it powered-on at its minimum rated operating temperature of -40deg C.
That should maximize storage life, but exactly how long the data would last in either scenario is unknown. The chip itself (but not the data) should last for centuries so if your object is to put the device in a time capsule then it would make sense to back-up the data to a more permanent media and include both a chip programmer and instructions to restore the data to the chip in the distant future