database is something different, it has nothing to do with 4images files.
your images also not .php or .html files, right? so if you dont touch them, then why would you loose them?
Besides that, I've never said anything about deleting anything, so you wont loose anything unless you delete something.
Trust me, if there would be a remote posibility loosing data during the upgrade, I would have mentioned that.
If you are so not sure, then why not create a test gallery with previous 4images version and then upgrade it, see if you loose anything.