The WC2BNE CD key can’t be linked to a Battlenet account. The generation/validation algorithm that was used with WC2BNE has been lost to time, meaning the modern Battlenet doesn’t have a way to read them. So the short answer is yes, WC2 would need to be bought again in order to use it through the launcher.
That said, if you don’t mind using the game’s shortcut to play, you can:
- Install from the original CD (using the CD key).
- Patch up to current. You can find patches on some of the fan websites. Just use discretion on where you get it from. I believe the most current patch is 2.02.
- For stability and graphic fixes, use “Patch #4” and for Battlenet functionality use “Patch #4” which can be found here.
At this point you’ll have the same version that those using the launcher have (with some stability fixes as well).
A-freakin-men