Shanks already made Akainu a "submitted lip-service" clown way back in MF so nothing would have changed in the situation of Shanks vs Akainu.
As for scabbard vs Akainu before Shanks getting involved, definitely a few would have gotten injured severely but Luffy and co. would also have arrived before any big incident took place (i mean casualties). Luffy knows difference between Akainu/Aokiji and other admirals. So he would have charged immediately after sensing his arrival.