Could an mri without contrast miss anything serious causing my daily migraines??

Yes: Some MRI's have stronger magnets and can see with better detail. Some foods cause headaches. You can google search the causes. Visit a headache specialist. Make sure it isn't allergies and sinuses/runny nose, glasses prescription or blood pressure issues. If you have a fever, visual disturbance Vomiting that is forceful, blurred vision, change in mental status are all obvious reasons to go to ER

Not really: MRI picks up things like brain tumors, abcesses, strokes, multiple slcerosis and other causes of brain inflammation. If your MRI was normal, there was definitely nothing serious. Migraines are due to a genetic abnormality in the electric activity in the brain and cannot be picked up on MRI. They rarely result in anything serious, although they are a major cause of disability and loss of job..

Unlikely,: but it is possible a small vascular malformation or other small lesion may not be identifiable without contrast.

Yes and no: Yes, MRI with contrast may pick up smaller nodules that enhance inccludinge small cancer nodules and small venous angiomas (VA). In practice, these are rear unless there is a history of malignancy in the case of cancer nodules. Small VA's present with bleeding which can be seen on non contrast MRI. It is the bleeding that causes symptoms. MRI contrast is safe. It increases lesion visibility

MRIs miss migraines: MRIs, even WITH CONTRAST, would not be able to diagnose a migraine. Migraines are diagnosed based on clinical exam and pattern of attack. A good Neurologist is 100x better than the BEST MRI in this situation. Most chronic migraines are idiopathic - they are caused by a functional change in blood flow, not an anatomic problem (like aneurysm or whatever). A neg MRI is reassuring, but not diagnostic.