There's an equivocation on the word Nirvana even within the Buddhist tradition. In the conventional sense it means a snuffing-out of anything, so you get words like parinirvana to refer to the final cessation of the processes that make up what we think of as a person. In that case it's a way of reframing death in the conventional sense. In the philosophical sense, Nirvana is not a snuffing-out but a way of looking at reality in which there are no entities that arise and cease--they "cease without remainder" (from our Samsaric perspective, at least) in that there never was anything to cease in the first place. That Nirvana is the conceptual opposite of Samsara. Buddhist enlightenment/liberation/Awakening is properly termed bodhi (the root of Buddha), but it is often associated with "realizing Nirvana," which is to truly understand the relationship between the ultimate truth of Nirvana and the conventional truth of Samsara.
Liberation from birth and death and enlightenment are effectively the same thing. To emphasize parinirvana as the ultimate goal is to misunderstand what Buddhadharma is about. That misunderstanding is probably very old, and it's probably at the heart of what the Mahayana sutras are polemicizing against--i.e. the idea that enlightenment leads one to cease to exist in the world, or to somehow escape from it. The emphasis on the bodhisattva path is a corrective, to remind people that the ultimate unreality of the self and the world does not mean that one does not continue to live in the world. One is not liberated from life or existence or even from the workings of karma. What one is liberated from is the perception that there is ultimately such a thing as existence vs. nonexistence, or that there is ultimately a thing called life that begins at your birth and ends at your death, or that there is anyone in particular who is subject to karma. Here is where people get caught up in the way things are framed in language, and why reading the scriptures in isolation, as if they had an inherent meaning apart from specific methods of interpretation, is perilous.