If you haven't closed Opera yet, goto the URL opera://about and take note of the "Profile" path. In the profile folder, copy the "Last Session" and "Last Tabs" files to a safe place like your desktop. Then, you can close Opera. You can then rename them to "Current Session" and "Current Tabs' and use them to replace the existing ones in the profile folder (once you close Opera). But, before you even try to do that, open the "Last Session" and "Last Tabs" files in a text editor to see the URLs of your opened tabs are even in there somewhere. If not, you're out of luck.
