The mage turns around the 'pass' card that he offered - and yet nobody he offered it to took. Unlike the second trial, he has lived to see another day. Despite knowing that so many innocents - friends - shall be struck down today because of the truth not being clear, of it being hidden: he promised them, didn't he? That he'd stay strong for them, and made it so that they didn't have to apologize to Yarne in his absence.
That he'd live, for them - so Bel and Izaya didn't get the satisfaction of watching everyone die. Yet, the disappearance of the robot child he watched over so carefully and diligently is but a stark reminder. One day, he'll vanish, too, in helping them achieve a good future.
(Maybe he'll get to see the robot child again then, and hug them and thank them, but the fact remains.) His existence in this world is limited, he knows. So what better way to honour his...friends and allies than to live to the best of each moment? Even though it'll be hard.
Madam Reika, after all, would want that as well.
"I'll keep my promise...and live for all of you. And you too, little robot chi - Percival."