If I downgrade my storage plan, will I lose my current backup?

Not right away, but if size of current backup or all backups exceeds allotted 5 gigs, at some point you will.

i have asked this myself the extra storage you purchase to have certain things to hold into the extra storage will expire between 30-60 days I was told.But typically 30 days I was told unless a company has requested a investigation like a CC Company.