I just finished OWB and I never got the option to let Dr. Mobius live. The only dialogue option to end the conversation was to kill him.
I did everything in Big MT gathered all personalities, helped every brain in the Think Tank, did all the sidequests and discovered every location.
Any one know if I might have missed anything?
Best Answer
The New Vegas Wikia notes a potential bug with this quest (verified on the PS3 release, although I imagine the same script issue occurs across platforms):
They suggest attempting the Repair check as a way to un-bug the dialog tree and get the "non-lethal" options back. If that fails, you'd probably have to reload an earlier save.
Past this quest, there's no real interaction with Mobius, so unless you really want a particular outcome from this quest, I'd probably suggest moving on if fixing it would be painful. There aren't any achievements, perks, items, etc, you'll miss out on.