I am very sorry to hear about the passing of your mother. But, if your father is exhibiting early warning signs of Alzheimer's you definitely want to get him checked out. Also, try and determine if his behavior changes are due to grief. We all grieve in different ways, but we shouldn't let grief and sadness interfere with taking control of our health.
If you're having trouble convincing him to get checked out, perhaps explain to him that with the recent loss of your mother, you don’t want to lose him as well.