Say I've played Gideon Jura's +2 ability:
During target opponent’s next turn, creatures that player controls attack Gideon Jura if able.
My opponent has attacked with Combat Celebrant and exerted them for another combat phase:
If Combat Celebrant hasn’t been exerted this turn, you may exert it as it attacks. When you do, untap all other creatures you control and after this phase, there is an additional combat phase.
On their first attack step, they attack Gideon Jura and he dies. Then on my second end step, what can they do?