I have done side by side comparisons in a cave, have you?
Actually I have, but that's not the question. The original question was wether or not you should continue a dive without a primary light.
The answer is simply NO! :no
Now, if you have a 3W light as a primary, that's your choice. But I would assume that if it died, you would thumb the dive and safely exit the system.
This isn't a discussion on light brightness, but primary light protocol.
Safe diving