If you want to be really sure you don't destroy anything accidentally, you should export your data before continuing. Sticking it in an Outlook PST will mean you retain all metadata and will allow easy import again should anything break (or you could use this to actually archive your stuff in to a seperate location).
With that suggestion out of the way, I think it depends on the type of account.
If you're looking at an Exchange or IMAP account that leaves everything on the serevr then nothing should be deleted - but you won't have access to them without the account setup.
If it's POP3 then Outlook is probably storing them in a local PST folder and this should still retain local copies - whether or not the server has copies depends on your configuration.
It will probably help if you clarify some things, although doing so may also lead to you working out the answer yourself. What kind of account (exchange, POP, other)? How are you intending to delete this account (simply stop send/receive, remove from Account Settings>Accounts, delete a folder which used to have these emails in)? Where are the archived emails (in a folder, in an archive.pst, some other place)? Can you simply take a backup of that [pst|folder|other]? – AdamV – 2010-08-18T11:20:12.540
Actually I am converting my pop account to imap, but it's not as simple as that: outlook doesn't support such a modification, it wants me to create a new account. This means I have to manually move all the mails from one account folder to the other. Secondly, my ISP automatically deletes inbox emails that are 1 year old. That's why I wanted to archive my +1 year old pop mails, move the newer ones to the imap account, activate autoarchive for that account, and finally delete the pop account as it's empty. I'd like to avoid exporting to pst because the mails won't be searchable anymore... – DavidD – 2010-08-19T05:13:59.423