Microfilms used to be sold as having a life expectancy of up 500 years. But in my experience they were a pain to use and the machines costly to maintain. The films would tear regularly too. Also the quality of the recorded image could be very poor sometimes.
Kinda relevant: from the latest Private Eye. Just a little insight to the background of the people pushing for this outcome.
The Heritage Foundation who would have guessed it would be in the mix.