If you have to time to plan it ahead of time you should give your employer plenty of notice. If it is an emergency surgery there is nothing you are they can do. If they let you go, you will have to claim unemployment, but you will receive it. Then you can find a better employer that will enjoy having a good employee. Best wishes and good luck. Note at least here this is a state where an employer doesn't need a reason to terminate it's employee. You may just want to keep that in mind.