I've (and traditional Theravada agrees with that) already shown that here "self of arahant" is meant. But seems you still can't get it.Don't say that, friend Yamaka. Don't misrepresent the Blessed One. It's not good to misrepresent the Blessed One, for the Blessed One would not say, 'A monk with no more effluents, on the break-up of the body, is annihilated, perishes, & does not exist after death.'
Remark by Ven. Bodhi to this sutta:
Spk glosses tathagata here as “a being” (satta), which I think does not quite hit the mark. I take the subject of the discussion to be, not a being in general, but the arahant conceived as a being, as a substantial self. Thus the catechism will show that Yamaka has abandoned his identity view (sakkaya ditthi) regarding the arahant, and there with his view of the arahant as a self that undergoes annihilation. We find a similar transition from the arahant (vimuttacitta bhikkhu) to the Tathagata at MN I 140,3–7 and I 486–88.