Did the Buddha die in absorption? I thought I'd just ask here: did the Buddha die in absorption / any of the dhaynas?
According to the Mahaparinibbana Sutta:


  And the Blessed One entered the first jhana. Rising from the first
  jhana, he entered the second jhana. Rising from the second jhana, he
  entered the third jhana. Rising from the third jhana, he entered the
  fourth jhana. And rising out of the fourth jhana, he entered the
  sphere of infinite space. Rising from the attainment of the sphere of
  infinite space, he entered the sphere of infinite consciousness.
  Rising from the attainment of the sphere of infinite consciousness, he
  entered the sphere of nothingness. Rising from the attainment of the
  sphere of nothingness, he entered the sphere of
  neither-perception-nor-non-perception. And rising out of the
  attainment of the sphere of neither-perception-nor-non-perception, he
  attained to the cessation of perception and feeling.
  
  And the Venerable Ananda spoke to the Venerable Anuruddha, saying: "Venerable Anuruddha, the Blessed One has passed away."
  
  "No, friend Ananda, the Blessed One has not passed away. He has
  entered the state of the cessation of perception and feeling."
  
  Then the Blessed One, rising from the cessation of perception and feeling, entered the sphere of neither-perception-nor-non-perception.
  Rising from the attainment of the sphere of
  neither-perception-nor-non-perception, he entered the sphere of
  nothingness. Rising from the attainment of the sphere of nothingness,
  he entered the sphere of infinite consciousness. Rising from the
  attainment of the sphere of infinite consciousness, he entered the
  sphere of infinite space. Rising from the attainment of the sphere of
  infinite space, he entered the fourth jhana. Rising from the fourth
  jhana, he entered the third jhana. Rising from the third jhana, he
  entered the second jhana. Rising from the second jhana, he entered the
  first jhana.
  
  Rising from the first jhana, he entered the second jhana. Rising from
  the second jhana, he entered the third jhana. Rising from the third
  jhana, he entered the fourth jhana. And, rising from the fourth jhana,
  the Blessed One immediately passed away.


Piya Tan's commentary here states:


  Samanantarā. Samyutta Commentary: Here there are 2 kinds of
  samanantarā: immediately after dhyana and immediately after reviewing.
  In the former case, one emerges from the 4th dhyana, descends into the
  life - continuum (bhavanga) and attains parinirvana. In the latter
  case, one emerges from the 4th dhyana, reviews the dhyana-factors
  again, then descends into  the life-continuum and attains parinirvana,
  as in the case of the Buddha. But buddhas, pratyeka buddhas, noble
  disciples, and even ants and termites pass away by way of the noble
  truth that is suffering, with a karmically indeterminate bhavanga
  consciousness (SA 1:224)


Dhyana is jhana. The difference between jhana and bhavanga is explained in  this answer:


  Jhana is more than just the giving up of the five senses. Each of the
  jhanas is the result of very strong samadhi, and has specific factors
  that go along with it. For example, the first jhana has five factors:
  rapture, pleasure, initial application of mind, sustained application
  of mind, and oneness of mind. As one goes deeper into the second
  jhana, one leaves behind initial application and sustained application
  of mind, and so on.
  
  Bhavanga is very different than this however. Bhavanga is like a blank
  slate. All it has are the mental factors that are necessary for mind
  to be there and nothing else. It only occurs in the space between
  other kinds of mindstate. None of the jhana factors are present at
  all, and there isn't even any meaningful degree of awareness in it.


So, according to these commentaries, the Buddha did not actually pass away in the fourth jhana. Rather he passed away in bhavanga.