Complex sentence: ABC's reformatting as "TV5" will take effect while the Finals is ongoing and the Fiesta Finals will be the last PBA event covered under the ABC name and the only PBA event covered under the TV5 name until 2013.
Split into simpler sentences: ABC's reformatting as "TV5" took effect while the Finals is ongoing. The championship series was the last PBA event covered under the ABC name and the only PBA event covered under the TV5 name until 2013.