Augurium Task Force gives a Purgation Squad more ways out of trouble than any other detachment in the faction.
Prescient Redeployment, the detachment rule. From the second battle round onwards, at the start of your Movement phase, if you did not max out Gate of Infinity at the end of your opponent's previous turn, you can remove one eligible Grey Knights unit from the battlefield and place it in Strategic Reserves. The Purgation Squad shoots from a good position for two turns, and the moment that position becomes untenable it simply leaves and sets up somewhere new.
Redirected Strike (1CP), at the end of your Command phase, puts a Psyker unit with Deep Strike into Strategic Reserves. The designer's note is explicit that this exists so you can score the objective and then leave.
Mirage of Echoes (1CP), in your opponent's Reinforcements step, does it reactively: when something drops within 12 inches of your squad, the squad vanishes.
Soul-Locked (1CP), from Fires of Purgation itself, is the fourth and the cheapest. When the Purgation Squad makes a fall-back move, that move does not prevent it being eligible to shoot. So even when it does get charged, it walks out and keeps firing.
Four answers to the same problem, from two detachments, and they cover different triggers: pre-emptive, end of Command phase, reactive to a deep strike, and after being engaged. A gun platform with this much escape is a gun platform that actually gets to shoot for five turns.