Zaros wasn't killed.
He was able to escape Zamorak's assault, at the cost of most of his energy and his physical form. Tho Jmods have said this is unique to Zaros.
We know Saradomin could project his form somewhere else, even while in the middle of battle with Zamorak.
We saw Bandos and Amascut create avatars to act in their stead. Bandos in Chosen Commander, but it cost him a lot of power when it was defeated. And Amascut in the 2015 H'ween event when she abused the soul power from the worlds brought by Tuska. So it's unlikely that it actually cost her anything.
So it is possible that a god could setup a scenario where they sacrifice some power to avoid getting killed (an avatar, a projection) and everybody notices it as the energy dissipates but doesn't leave behind a stone body, possibly leaving others fooled or simply giving the other party a chance to vent frustration in story without Jagex canonically killing off a character and the character saying they
knew
it really wasn't X but it still felt good to blast it.
Could Zaros escape again like he did last time? yes. But it took him thousands of years to rebuild his energy feeding off Mah and he needed help from the World Guardian to make a new body. With the Elders waking up soon, and Mah out wandering the universe, while he would survive, he wouldn't be in a position to try to prevent the next Great Revision.
18-Sep-2016 19:51:20