Put another way, assuming he has mental capacity, he can write you in or out at any time and you do not have the right to find out until he dies.
A will can be successfully challenged only where it is demonstrated that the person who wrote it, the testator, lacked testamentary capacity or was incompetent. Overturning a written will requires demonstration either that there was a lack of capacity, or that there was undue influence exerted by another person to the point that the signer lacked judgment to know what they were signing, or both.
Wills are changed all the time and no offspring has the "right" to be in a will. In fact, I find that people who think they have this mythical right are the same people whose parents often disinherit, as many parents are annoyed to learn that a child expects an inheritance.
The best advice is to treat dad right, help him as much as possible and the chips and the house will fall where they may.
• • •
Andrew Myers of Derry has law offices in Derry and North Andover. He is a member of the American Association for Justice and the New Hampshire Trial Lawyers Association. Send questions to firstname.lastname@example.org.