Kinemon's death would have worked greatly towards making Kaido seem more ruthless, because in the end the Yonko who talked to much about life and death and who himself admitted that the alliance won't stop until he showed them Luffy's head, ended up killing nobody important.
Kinemon dying there would've rendered the war more realistic. His death would've likewise pushed Momo to trying his best.
Plus, Oda had the perfect set-up with the flame festival for bringing Kinemon's ghost back after the war for a last pep talk to Momo.