Vraska disclosed Bolas’s bargain and Jace understood how the Immortal Sun fit beside the Eternal army and Planar Bridge. Tezzeret arrived through that bridge to retrieve the artifact, proving the pieces were already being assembled. Once the Sun left Ixalan, the barrier against planeswalking disappeared.
Openly refusing Bolas would have made Vraska disposable. Jace therefore placed the truth of their alliance behind a mental trigger, then removed her accessible memory of it. She could return to Ravnica, take control of the Golgari and appear to have completed the mission without carrying evidence Bolas could extract.
Jace departed with his identity restored but changed by the person he had been without it. Vraska returned to a role inside Bolas’s strategy while holding, beyond conscious reach, the means to choose differently later. The Sun Empire claimed Orazca, yet the artifact at the centre of the race had already become part of a war on another world.