Complex sentence: Gothel agrees, but before Rapunzel can heal him, Flynn cuts her hair which subsequently turns brown and loses its power causing Gothel to age rapidly, fall out of the tower, and turn into dust.
Split into simpler sentences: Gothel agrees, but before Rapunzel can heal him, Flynn cuts her hair which subsequently turns brown and loses its power. Gothel, in turn, begins to age rapidly, falls out of the tower, and turns into dust.