Aside from a rupture, when is emergency surgery needed for a brain aneurysm?

Aneurysms leak . Aneurysms leak before rupture: sudden paralysis of the nerve to the eye, sudden headache due to enlargement of aneurysm can be detected on MRI or lumbar puncture before catastrophic rupture.
Depends. If the diagnosis is accurate and the indication is clear (size of it and localization) i would not wait until catastrofe knock on the door. This usually happens in the 4th decade of life. Please consult you neurologist and/or neurosurgeon. I am not one of them.
3rd nerve palsy. Other than a rupture, the sudden onset of a dilated pupil on one side can herald the rupture of an aneurysm. The 3rd nerve is right up against the site where an expanding posterior communicating artery resides.If the aneurym grows but does not rupture, it can lead to the sudden onset of a dialted pupil (in the abscence of trauma). This should be investigated and treated immediately.