but only momentarily
I never said that. Though you could, without lying.
"Nirvana" is not a place, it is not a tangible thing, it is not anything material. Is itself, in a literal fashion: a "blowing out," as of a candle. It is a non-thing, a lack, a non-existence, insofar as it is an "is."
In other words, it's nonsense to talk about the existence or non-existence of Nirvana. The most efficient--that I can muster--way to describe this nonsense is by describing Nirvana as a non- without the qualities necessary for an existence, without a Dasein, if we are to cross cultural borders.
That is, certainly, an inaccuracy, but only direct realization, personal experience of Nirvana can transmit its nature (or lack thereof, whatever) to a seeker. The descriptions are all inherently weak, flawed: imperfection is a seal of existence, but Nirvana is not within the confines of existence, and thus is not bound by the imperfection which surrounds our concept-laden existence.
That's the long answer. The shorter answer would have, I guess, just been a link to Joshu's Mu. A dog does not have Buddha-nature.