possible miel was abroad several times during recording and anyway there were not loads of options for group
miel will surely get two songs on next album if he is still there (hopefully) people say he should leave but i believe he should remain a bit, he did not make the expected rise to cover heritier's departure since he was often abroad and the group was understandably shaken by heritier 's departure and like all the other groups by the political issues which had got attention of people on music down a bit
so for me now he seems like being eager to make that step up,so he should do maybe one two more albums really cement something strong and then go solo peacefully
as for diego i believe the issue is also his voice, you'll notice than even in his short part there is serious autotune while the real diego was going as high as the old celeo if not higher at times