This is a very complicated situation.

Of course, you can sue him for all your damages, but is it really malpractice is something the court has to decide. Also the court has to decide the damage. It may be less than you otherwise would get had the will not been defective. If you prevail in the court, his insurance company will have to pay. If it is still not enough to cover all your damage, the attorney will be personnally liable for the difference.