
ausbleiben
to fail to appear
Not to take place, not to happen, or not to arrive, although it was expected.
Der erwartete Erfolg der Kampagne ist leider ausgeblieben.
The expected success of the campaign unfortunately failed to appear.
to fail to appear / to be absent
Loading your saved state.

to fail to appear
Not to take place, not to happen, or not to arrive, although it was expected.
Der erwartete Erfolg der Kampagne ist leider ausgeblieben.
The expected success of the campaign unfortunately failed to appear.

to be absent
Specifically in a medical context: the absence of menstruation.
Wenn die Regelblutung ausbleibt, kann das ein Zeichen für eine Schwangerschaft sein.
If menstruation is absent, it can be a sign of pregnancy.
'Ausbleiben' (to fail to appear / to be absent) is a separable verb. In a main clause, the prefix 'aus' goes to the end of the sentence. In subordinate clauses or in the infinitive, the verb stays together.
Die versprochene Gehaltserhöhung blieb leider aus.
The promised salary increase unfortunately failed to appear.
The perfect tense of 'ausbleiben' is always formed with the auxiliary verb 'sein', not with 'haben'. This is because it describes a change of state—from something expected to something that did not happen.
Der angekündigte Regen ist den ganzen Tag ausgeblieben.
The announced rain failed to appear all day.
You can recognize the meaning from the subject of the sentence. If the subject is 'die Regel' (period) or 'die Periode' (period), the word has a specific medical meaning. With all other subjects such as 'Erfolg' (success), 'Antwort' (answer), or 'Gast' (guest), it has the general meaning of 'not happening' or 'failing to appear'.
Eine Entschuldigung seinerseits ist bis heute ausgeblieben.
An apology on his part has failed to appear to this day.
to be absent / to be missing
Fehlen describes an expected person not being present. Ausbleiben emphasizes more strongly that the person’s expected arrival does not occur. Fehlen is appropriate for the state of being absent; when the futile waiting or failure to arrive is important, ausbleiben is appropriate.

Der angekündigte Redner bleibt trotz des Beginns der Eröffnung aus.
The announced speaker fails to appear even though the opening has begun.
Der angekündigte Redner fehlt bei der Eröffnung.
The announced speaker is absent from the opening.