It is not oxidisation that is the issue. Humidity and temperature are the main issues. Film is metallic silver in gelatine, and lasts ok, but thousands of years is a very long time.
They do mention a metallic storage system which should last a vary long time. I suspect the microfilm was there more for publicity than any real expectation that it would work in 8000 years. Still even if you can't directly read them they may degrade in such a fashion that you can reconstruct a useful significant percentage of the original message.
A backup metal film system resides in the crypt as well.[1][2]
[1]"The New Georgia Encyclopedia — Crypt of Civilization". Retrieved 2008-06-29.
[2]"History of the Crypt of Civilization". Retrieved 2008-06-29.
