disappearance vs leaving

disappearance and leaving both are nouns.

Word	Noun	Adjective	Verb	Adverb
disappearance	Yes	No	No	No
leaving	Yes	No	No	No

As nouns, leaving is a hypernym of disappearance; that is, leaving is a word with a broader meaning than disappearance:

Other hypernyms of disappearance include departure, going, going away.

disappearance (noun)	leaving (noun)
the act of leaving secretly or without explanation	the act of departing
gradually ceasing to be visible
the event of passing out of sight
ceasing to exist