As to time, magnetic recordings will erode over time and when the error correction can't correct for the missing bytes then playback of that section will fail.
It is possible to move such to non-magnetic storage for longer storage.
I will like to get this issue clarified. I know that digital video means that the media is digitised ie. everything is converted to digits.
Is this what happens when you record on a DV tape?
Also the analog tape loses quality over time with sound lines being added to the tape. What happens to a DV tape over time?