I don’t understand.
I think the musical episode will still have flashbacks, with songs in both flashbacks and present day. Not sure how they’re going to explain that, if they do at all.
I think the only way to explain it would be a la Buffy style, a one-off villain comes to town (and the EF) and causes everyone to burst into song.
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"He was a lot of things to me" "The only conclusion was love"