Bit rot is a real problem, but HDD are consumer products with very poor sensors. Assuming similar levels of technology Data should be recoverable for hundreds of years.

File formats in general are fairly straightforward at the bit level. Languages would be a larger issue except they are also stagnating with slower drift over time as population sizes increase.

On top of that we are still producing vast amounts of written material that is likely to survive. Net result future historians are going to have far more to work with than current ones do.

PS: Remember even 1 in 1,000,000 files would still add up to a lot of information. That said, encryption is likely to be a larger issue.