What happens if Imakuni?'s Doduo is KO'd or retreats with "Frenzied Escape" while singing for its "Harmonize" attack?
The singing continues and the damage is placed when the song is finished. Just because Imakuni?'s Doduo is not in play doesn't mean its attack stops.
Source: Evolutions FAQ (2016-11-03), TPCi Rules Team (2016-11-03)

Relevant cards

Note: All applicable cards may not be listed below.
XY12_112