The second opening for 四月は君の嘘 starts with these two lines:
忘れようとすることで傷が癒えないのは
忘れようとすることで思い出されるから。
I get the feeling that something is missing after から, like だ or です. Is this sentence still grammatically valid? Also, are the reasons for this omission as I suspect them that ending a sentence in plain だ is unusual and that a formal です would be out of place in such a song?