All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
An-Najaashi died in the year 9 AH, as has been favored by Ibn Hajar as he said, “His death occurred in the year nine after Hijrah according to the view of most scholars.”
The Sahaabah (Companions) who remained with An-Najaashi returned to the Prophet two years before that, and they were Ja'far and those with him.
So this statement appears to be true; that no Companion remained to offer the funeral prayer for An-Najaashi.
This discussion was ongoing among the scholars regarding the issue of the funeral prayer for an absentee. It is a very long discussion, but this is our reply to what was mentioned in the question.
Allaah knows best.