Co-Worker Too Sick to Be Working

So if Sicky Dude moved.....who gets the promotion to his position?

Wow...just...really?
The company is likely taking a hit to their bottom line to ensure one of their own keeps his medical coverage during what is likely the last stages of his life and OP wants him gone because it bothers him...By all means take your concerns to HR or your boss and let them know how you feel.

I could see concerns if he was operating heavy machinery or the stress of the job was worsening the condition but none of that was mentioned.