Complex sentence: The band saw the scout at the venue and was disheartened when he left mid-set, but it turned out that the scout had left to phone the record label and to tell them to sign Pantera as soon as possible.
Split into simpler sentences: The band saw the scout at the venue and were disheartened when he left mid-set. It turned out that the scout had left to phone the record label and to tell them to sign Pantera as soon as possible.