The fight would be over even before sage mode, that's if he starts in base mode.
If he started in sage mode, then he might be able to take pein by surprise with frog song, but then since plot didn't let him sense the other 3 pein(s), he'll probably not see/sense them and the result would be the same. Though if he starts in sage mode and he fights all 6 peins at once then he might actually win with frog song.