I'm sorry for your loss, but am speechless at a litter box not being changed for 11 days!

Your cat may have just died from old age, but when a cat stops eating or drinking it is very serious and the cat needs to be taken to a vet ASAP. The mucus in the eyes can be a sign of an Upper Respiratory Infection that can be fatal if left untreated.

Again, I'm sorry for your loss.