so you've told FCP to forget the files, and you're not getting a warning anymore?
well before you render/export, the offline files will be fairly prominent in the timeline.
they will be WHITE in colour, with (prior to rendering) a RED render bar above them.
if you want to make really sure your sequence is all on-line,
control or right click on it in the browser,
and choose "reconnect"
at the top of the reconnect window that opens you can choose to display online, offline, or render files.
if there is anything offline you'll soon find out.
nick