What is a file?
And where do they live?
Today they live on flash drives, phones, tablets, compact flash, SD cards, hard drives, solid state drives, optical discs, tape and now they commonly stay in reach via a concept known as the cloud.
How long do they last?
That's a tricky question to answer because it depends on a few factors:
Can the the file be found? And does anyone want to find it?
Has it been catalogued in some manner with metadata?
Is the file still readable by an operating system and application?