Buddha wrote:"This teaching doesn’t lead to disillusionment, dispassion, cessation, peace, insight, awakening, and extinguishment. It only leads as far as rebirth (viz. to cause to fall towards*) the field of neither perception nor non-perception.'
"nāyaṁ dhammo nibbidāya na virāgāya na nirodhāya na upasamāya na abhiññāya na sambodhāya na nibbānāya saṁvattati, yāvadeva nevasaññānāsaññāyatanūpapattiyā’ti."
*Note that upapatti does not really mean "rebirth" (among) - but instead, it literally means "to cause to fall towards".
That is to say that the Buddha still believed that, this was way below the final stage of nibbāna. Namely a debasement from vijja.
Yet, that does not necessarily mean that Āḷāra Kālāma & Uddaka Rāmaputra were annihilationists.
Nor does it necessarily mean that they believed that they could be reborn in that state, after death.
There is no surety about that.
.
.