Gideon Jura vs an opponent with multiple combat phases

Question

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?

Answer 1

Gideon Jura creates a requirement that they attack him if able.

In the second combat step, Gideon Jura is no longer around and able to be attacked, so they have no need to attack him. The player may attack freely, including you directly or any other planeswalker you control. They may also not attack at all since they have no more requirement to do so.