Allah Almighty says to the Prophet (sws) that he will also leave this world as the previous prophets did. A ḥadīth is very commonly known that Prophet said a Muslim must visit his grave to say asslamaulaikum when he comes for Haj or umrah. If this narrative is authentic, then don't you think it is in contradiction of the verse I have referred to above?
Secondly a firqah amongst Muslim strongly believes in intercession through awliya Allah who are dead and probably their argument is based on what I have written above. I may clarify here that I am not interested in going into any sort of argument with believers in intercession, just want to know the truth:
(1) saying assalamu alaikum to the Prophet (sws) which he listens and
(2) on what basis we can connect the similar listening of assalamu alaikum by awliya Allah?