Complex sentence: After he left the group, the band felt they were at a musical crossroads; although they considered replacing Avery, they ultimately decided not to replace him and, after playing a few concerts without him, felt they needed to step it up musically.
Split into simpler sentences: After he left the group, the band felt they were at a musical crossroads; although they considered replacing Avery, they ultimately decided not to replace him. After playing a few concerts without him, felt they needed to step it up musically.