As far as I know, dropbox has no such "public" folder, it just syncs to a folder on my computer, and the downloads will only ever disappear if I personally get rid of them.
This has been put in my _permantent folder, however.
Who knows what could happen though, better grab it before it randomly disappears ;p
I own a community of TF2 servers
ASMT - A new revolutionary ASM system, aka 65c816 ASseMbly Thing
SMWCP - SMW Central Presents a Product- tion long name