Yes all brain aneurysms can become life threatening if they get to the point of rupturing which in most cases the brain aneurysms can and do rupture.
That's when the aneurysm becomes life threatening.
Aneurysms usually come on without too many warning signs until they do rupture but some symptoms of an aneurysm before rupture are headache or pain behind or above the eye, which can be mild or severe.
If you think you may be experiencing an aneurysm then you really do need to see a doctor or go to the emergency room before it does rupture and potentially causes death or other brain damage.