I am interested in removal of lipoma using Kybella injections. How successful would this operation be?

I would not recommend your approach. Forhead lipomas are almost always deep to the frontalis muscle. For most people and horizontal incision directly over the lipoma if done correctly by a meticulous surgeon will heal with a almost imperceptible scar. It is the most forgiving area on the body in regards to score formation. The scars are rarely anything compared to what the lipoma looks like for most people. For women to wear make up it’s a no brainer.
The contour deformity that a lipoma gives trust a shadow that can be seen from across the room. Because the scars tend to blend and fade out almost completely and leave zero deformities in regards to contour they are barely visible unless looking from very close under scrutiny.
Kybella Has he substantial chance of leaving a contour that is unpredictable and may not at all be what you had hoped for. 
Direct excision is an excellent option and would most likely give the best results in a very predictable manner.
if you talk to providers who are not board-certified plastic surgeons and use Kybella Like a nurse in a med spa and then you were most likely be told this is a good option.
I seriously doubt any board-certified plastic surgeon would say that your proposed treatment is the correct one.
Scars are very predictable from examining a patient’s skin complexion and seeing how they’ve healed from other cats, scrapes or previous surgeries. everyone has some tiny little scar someplace on their body that we can examine to predict what future scores will look like. because the four head is so forgiving what the square will look like is highly predictable. unless you have a skin complexion that’s unfavorable for healing surgery is straightforward and should be the way to go.
just my opinion.
Best,
Mats  Hagstrom MD