I would stay with him because I love him and in a way, what you have described has already happened. My husband and I have been together for a little over sixteen years. When I met him and fell in love, we were both Juniors in high school and his body was smooth and hairless save for a small, struggling mustache. He had a gorgeous head of long brown hair with flecks of gold that glowed in the sunlight. He was lithe and agile, able to scale high ladders in the school theater to clamber around on the catwalks adjusting and tweaking the lighting for the next school play.
I was also very different then myself. As we've aged, the skinny goofy boy I fell in love with bloated into a large jolly man with short thinning hair. His once smooth, hard young body has softened and sprouted a forest of hair. I myself have warped and altered since high school, having gone through a pregnancy and two surgeries.
Life and the progression of time has forever altered us and stolen that which we once loved and cherished about each other, yet over the years our love has also changed and grown to accommodate our new selves.
Some day far in the future, the physical things that we once loved about ourselves today will be gone completly to be replaced by sagging wrinkled skin and thin white hair, if the hair sticks around at all...
So yes, if my husband lost limbs and became difficult to care for or some crazy nut thew acid in my face to irreparably disfigure M., we would still continue to love and care for each other because at some point in our lives we stood up and made a promise to each other. In times of sickness and in times of health, in times of joy and in times of sorrow, in times of failure and in times of triumph. I promise to cherish and respect you, to care and protect you, to comfort and encourage you, and stay with you, for all eternity.
Time, like a thief in the night, will sneak in and slowly steal away whatever physical qualities you love about your significant other. It's inevitable so when you chose a mate, make sure you love more about them then their beautiful long hair or amazing singing voice. It is all vapor that will blow away in the blink of an eye.
If you ask, "Would I ever fall in love with someone who was disfigured at the beginning of the relationship." My honest answer is, "I would be repulsed by deformity and disfigurement like anyone, however, I am one able to be won over by personality and promises of devotion so it's possible had someone terribly deformed come onto M. and been persistent, I may have eventually come to love them and bind myself to them forever."
When I was young I had a crush on the phantom of the opera, a tragic and deformed character.