A true Existentialist marvels at the thought of having the option of choosing the time, place and method of erasing oneself.
But the instance suicide is committed, he is no longer an existentialist.
It's better to be an existentialist as long as possible. Even if it becomes absurd. To maintain life is to maintain my philosophy. Suicide is forfeiture of the very thing existentialists cling on to-their ego created as a defence mechanism against all man created banalities.
"Il n'y a qu'un problème philosophique vraiment sérieux: c'est le suicide" I guess.