The concept of a “Final Sickness” is part of the Islamic Rules of Inheritance and unlike what you might find anywhere in American law.
Let me take you back a little bit to describe what I am talking about, to a time in Europe when the Church was increasing its power and wealth in Europe. A man with an estate and children is dying. Clergy visits him. They tell him that if he were to grant all is property to the church, he will be granted absolution. The man agrees to this. When you are about to die, absolution is a very good deal. If that means impoverishing your family, so be it.
You see, at the deathbed, there is a long history of people doing wacky things. They seem to be more easily manipulated and subject to elder abuse. Things outsiders suggest to them start to “make sense” when they would not have before hand.
The Islamic Rules of Inheritance recognizes this tendency among human beings. So in a “final sickness”, the rules that govern the alienation of property change. Normally, you can part with your money in the manner you see fit. There are a number of Companions of Muhammad (SAW) who gave away all of their assets during their lifetime. This is normally not a problem. Giving all your wealth to a religious institution, a hospital or to whomever you want is typically fine.
Yes, if you are healthy, you are unlikely to give away all your money, especially if the wealth is substantial. In general, people are more afraid of running out of money before death then they are death itself. But some people give these large gifts and it is not a concern is Islam, most of the time. Deathbed gifts are regulated. Of course, a Muslim can never really change an Estate Plan based on the Islamic Rules of Inheritance. A new rule that comes up is they cannot give things greater than what they may give in a wasiyyah, which is 1/3 of the Estate.
The rights of the family as specified in the Quran (4:11-14) take precedence over anything else, including a desire to give to charity. Remember: Inheritance in Islam is not about you or what you want. It is not even about you family. It is about a peaceful and cohesive society with a consistent set of rights. Allah ordained these rights. Muslims don’t second-guess them.
What is a final sickness though? An illness that would reasonably lead to death within one year is a typical answer. So having an illness doctors say is ultimately fatal with a longer life expectancy than one year does not result in the final sickness restrictions in Islam. This has important implications. For example, Alzheimer’s in its early stages is not typically a “final sickness.” People with this particular illness may live several more years and have the ability to competently do their estate planning and gifts for several of those years.
Muslims who are in a “final sickness” can and should do their estate planning and make sure their assets are distributed consistent with Islam. It is just as mandatory for them to do this as it is for anyone else. Indeed it is more imperative for family members to push them to do this. This is when they are subject to some great pressures and they can more easily be subjected to manipulation by the unscrupulous. Even if this were not the case, Islamic Inheritance would be vital in order to maintain peace and harmony in your family, and because it is fard. Just like it is for everybody else.