It was reading the docs that got me worried, it says,
"Warning: If you already have users and custom groups in your coppermine database when you enable bridging, be aware that they will be lost. If your coppermine users have already created private albums and uploaded pics to them, they will be lost as well!"
You should read on, as that section explains that you actually don't lose anything, but only the correlation between user actions and user IDs. Once you turn bridging back on, everything will be back to normal again. You can toggle bridging off and on and off and on: as long as you return to the state that your gallery used to be when the database content was generated, everything will be fine. If there was a danger in upgrading whil being bridged, we'd warned you about that danger in the upgrading sections of the docs.
Now as I'm using bridge for SMF 1.x.x then upgrading to SMF 2 I have to use the bridge for SMF 2. Will I still retain all the contents of my gallery? or will I lose it all as stated in the docs?
No, for Pete's sake: you won't lose anything, as the user IDs will not differ. Again: read the details:
Coppermine users, groups and pics uploaded by users are lost when integrating
Warning: If you already have users and custom groups in your coppermine database when you enable bridging, be aware that they will be lost. If your coppermine users have already created private albums and uploaded pics to them, they will be lost as well!
Detailed explanation:
As most community applications, coppermine stores everything that users (including the admin) do (like uploading pics, posting comments, rating files) inside the database. The reference to each user action is being kept using a unique user ID. The correlation between the user actions and the corresponding user profile is being kept by storing the user ID within each record in the database that determines the user action.
When bridging is enabled, coppermine's user management is being dropped in favor of the user management that comes with the application you bridge with. Subsequently, the user IDs from your bridging app (that differ from Coppermine's user IDs) are being taken into account.
Coppermine-user "Bill" has got the coppermine user ID "3". He used to upload several pics that went into the folder /albums/userpics/10003/. The URL of his personal gallery used to be http://yoursite.tld/your_coppermine_folder/index.php?cat=10003.
In the BBS application, the user "Linus" has got the user ID "3".
After enabling bridging, the URL http://yoursite.tld/your_coppermine_folder/index.php?cat=10003 points to the personal gallery of the user "Linus". All pics that Bill used to upload appear to be owned by Linus.
Summary:
Correlation between the actions that the unbridged coppermine users have performed and the "new" accounts from the app you bridged with is lost. Subsequently, you don't actually lose files that have been uploaded previously, but they appear to have been uploaded by a different user.
Bottom line: if you're afraid that something fishy might happen, then perform a backup both on file as welll as database level before you upgrade. This way, you can savely go back in case something goes wrong.
Please stop the discussion now: nothing bad will happen when upgrading!