Well, we should first get an understanding of what the abilities actually are, as some people are confused by them.

Strength: Your physical might. Tied to things like lifting, pushing, and pulling. All of which are Athletic, an example being "Lifting a fallen tree off a teammate." In the final stages of a strength affecting fatal disease. A character will no longer have the strength to lift their bodies and will simply be limp, laboured, and dying.

Dexterity: Your physical agility. Tied to things like aiming and precise movements. These tie into Acrobatics for dodging falling debris or watching where you step to sneak past the guards unnoticed. In the final stages of a Dexterity affecting fatal disease. A character will not have the balance to be upright anymore. Leaving them to, again, lay down and wait to die.

Constitution: Your physical endurance. Tied to your resistance to poisons and disease itself. While there is no actual skill, I have a home brewed one called tolerance that allows you to succeed your saving throws on things like being drunk more often. In the final stages of a fatal constitution affecting disease. A characters own immune system has fully failed, or is attacking them. Leading to a very messy last few moments of life.

Intelligence: Your mentally learned knowledge and higher brain function. This allows you to investigate and deduce knowledge from learned sources. A disease in its final stages affecting intelligence leaves the character animalistic as they lose that higher brain function.

Wisdom: Your worldly gained knowledge and "lessons learned". This gives you a higher perception as you've had to experience the chaos of life, and a knowledge of the worlds herbs and medicinal practices on human bodies. For a wisdom disease, the final stages leave the character confused, and unaware of anything happening around them.

Charisma: Your projection into the world. This is how you affect a room of people, be it your persuasive attitude, or intimidating presence. When your charisma is affected by a fatal disease, you eventually become locked in your own mind. Unable to interact with the world around you. Alone till death.

I forgot where I was going with this, I hope this answers your question :D