Complex sentence: On 15 August 2017, Bob Katter, the founder/leader and sole MP of Katter's Australian Party, announced that in the event Joyce's seat is declared vacant, he could not assure that he would support the Turnbull Government on confidence and supply.
Split into simpler sentences: On 15 August 2017, Bob Katter, the sole MP of Katter's Australian Party, announced that the Coalition could not count on his support if Joyce is forced to give up his seat. Katter said that in the event Joyce's seat is declared vacant, he could not assure that he would support the Turnbull Government on confidence and supply.