The noun disappearance can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be disappearance. However, in more specific contexts, the plural form can also be disappearances e.g. in reference to various types of disappearances or a collection of disappearances.

What type of noun is disappearance?

The action of disappearing or vanishing.

Is existence countable or uncountable?

[uncountable] continuance in being or life; life: It was a constant struggle for existence. [countable* usually singular] mode or way of existing: They were working for a better existence. [uncountable] all that exists: Existence shows a universal order.