How does one respond to those who cite the Prophet's return of the greeting of "peace" to him after his death as proof that he is alive?

The prophets are alive in their graves with a barzakhi life whose true nature is known only to Allah, as established by the hadith: "The prophets are alive in their graves, praying." And the earth does not consume their bodies, as stated in the hadith: "Indeed, Allah Almighty has forbidden the earth from consuming the bodies of the prophets." Our prayers and salutations reach them, as he said: "There is no one who greets me with peace except that Allah returns my soul to me so that I may return his greeting," and his saying: "Indeed, Allah Almighty has angels who roam the earth and convey to me the greetings of my ummah." This does not, however, permit seeking their aid (istighathah) or supplicating to them, for supplication (du'a) and seeking aid (istighathah) are acts of worship that are due to Allah alone.