What is the grammatical form of "Memosei"?
Radak: It is a noun, like ki'Mevo'ei Ir Mevuka'ah" (Yechezkel 26:10). Without the extra Mem it would say Mosei Chala'im Tamus; it is the plural of Maves. They will die from illnesses, i.e. illnesses of starvation. This is like it says above (14:18), "v'Im Basi ha'Ir v'Hinei Tachalu'ei Ra'av." Also Yonason translates 'people sick from hunger will die.' If it would not mean so, why would it say "death of illnesses they will die"? All people die amidst illness, if not from the sword!
Why will they not be eulogized or buried?
Radak: Everyone will be obsessed with himself. He will not have time to eulogize or bury.
Malbim: They will be afraid to touch them after death 1 .
This explains why they will not bury them (perhaps their illness is contagious). Why will they not eulogize them? (PF)
Why will they be fertilizer on the ground?
Malbim: Chayos will not be found to eat the bodies. Afterwards, via sword and hunger, the remaining people from the plague will be eradicated, and then birds and Chayos will be found to eat their flesh.