Is accounts.ini missing the feeds account? (there should only be 1 feeds account in there,)
One way to fix accounts.ini (besides restoring from a backup) is to recreate all the account sections in the exact same order as they were before.
For example, launch the Opera installer, click "options", set "install path" to a folder on your desktop, set "install for" to "Standalone Installation (USB)" and install. Set up your mail accounts in the exact some order as you did before. And, subscribe to a single feed to create the feeds account in accounts.ini. But, don't subscribe to the feed until the right time. For example, if the feeds account is supposed to be account 3, you'd subscribe to the feed after setting up the first 2 mail accounts.
Then, close that Opera. You can then use its account.ini to replace yours.
The catch here is that you have to remember the exact order you did things before.
For index.ini, what do you see wrong with it specifically?