I am not really satisfied. I want to share this with you:
For me the clue is that an arahant or Tathagata, even while living, cannot be reckoned to be the khandha’s. One cannot say anymore that an arhant is rupa, vedana etc or some combination of those.
This is told in MN72
20. “So too, Vaccha, the Tathagata has abandoned that material form by which one describing the Tathagata might describe him; he has cut it off at the root, made it like a palm stump, done away with it so that it is no longer subject to future arising. The Tathagata is liberated from reckoning in terms of material form, Vaccha, he is profound, immeasurable, unfathomable like the ocean. The term ‘reappears’ does not apply, the term ‘does not reappear’ does not apply, the term ‘both reappears and does not reappear’ does not apply, the term ‘neither reappears nor does not reappear’ does not apply”
The same is said about vedana, sanna, sankhara and vinnana.
Maybe some think the Buddha talks about the future but that makes not sense for me. The Buddha talks about the present. Even while living a Tathagata (and arahant) cannot be reckoned anymore in terms of the khandha’s. And this is also true for us, but sakkaya ditthi, sets the trap that we think we are rupa, vedana etc.
Also SN22.85 has the same thema:
“What do you think, friend Yamaka, do you regard form as the Tathagata?” – “No, friend.” – “Do you regard feeling . . . perception .. . volitional formations … consciousness as the Tathagata?” – “No, friend.” “What do you think, friend Yamaka, do you regard the
Tathagata as in form?” – “No, friend.” – “Do you regard the Tathagata as apart from form?” – “No, friend.” – “Do you regard the Tathagata as in feeling? As apart from feeling? As in perception? As apart from perception? As in volitional formations? As apart from volitional formations? As in consciousness? As apart from consciousness?” – “No, friend.”
“What do you think, friend Yamaka, do you regard form, feeling, perception, volitional formations, and consciousness [taken together] as the Tathagata?” – “No, friend.”
“What do you think, friend Yamaka, do you regard the Tathagata as one who is without form, without feeling, without perception, without volitional formations, without consciousness?” – “NO, friend.”
“But, friend, when the Tathagata is not apprehended by you as real and actual here in this very life; is it fitting for you to declare: ‘As I understand the Dhamma taught by the Blessed One, a bhikkhu whose taints are destroyed is annihilated and perishes with the breakup of the body and does not exist after death?”
When a arahant or Thatagata is only rupa, vedana, sanna, sankhare and vinnana, apart or all taking together, and nothing else, then is is quit clear a Tathagata does not exist after death.
The clue seems to be that even while living an arahant and Tathagata cannot be reckoned this way anymore.