Technically speaking - err  YES.

cease to exist in the 6 planes of existence in which the cycles of birth and rebirth occur.

gods realm > "heaven"
demi-gods realm > "heaven"

human realm > "earth"
animal realm > "earth"
hungry ghost realm > "earth"

hell realm > "burning hells"
to achieve enlightenment and ascend into higher planes of existence.
to escape from this maze we call earth.

Technically speaking - err  YES.

all the 6 planes i mentioned earlier are subject to cycles of birth and rebirth oh.
must ascend higher.

no, them dewa and semi-dewa in the heaven realm still need to cultivate one.
not buddha yet.
still can reincarnate one.

refer to "mulan" story.
mulan was a sky soldier in heaven realm that got reincarnate as a lady in china, ancient war times.

yes, buddha amitabha achieved enlightenment and ascended above the 6 realms of cycle of birth and rebirth.

well, what lies above the 6 realms, i dunno liao.
and no, i dun think it is nothingness.

just higher planes of existence i think.
ceased to exist in the 6 lower planes of existence.

dewa
semi dewa
manusia
binatang
hantu lapar
neraka
still exist in the higher realms.

That's my 6 realm