If your mother is his legal wife, she has some protection from the state to protect her in this sort of situation. She can always contest, even if she wasn't married to him, especially if you lived with him as his child. You would have some protection, too. If there is anything of value, house, savings, etc., she should see a lawyer. I know of 2 cases where the will was changed by the court.
This is a failure on your mom's part. If he didn't update the will, then sorry. The consolation is your mom is not responsible for funeral or burial costs. Get her to a lawer really fast. There are many you can call on Sundays.
Shorty pay attention, don't worry if the will was mad before he married your mom, it also depends on what state are you in, because if your mother and your step father were married legally and depending what state you live in what ever your step father owned that belongs to your mother now. But it's always very good idea to speak to an attorney.
In some states when you marry the house becomes marital property. So if he owned the house and left to someone else she may have some right to the home. But everything else in the will would remain valid like with money or possessions. I would talk to a lawyer if there is a home involved otherwise she gets nothing if not stated in the will.
In most cases the house is automatically given to the spouse regardless of will. Everything else is distributed as per the will. You can contest it but since the house was her legal dwelling it will be hard to take it away from her. At most you will receive half the house until she dies.