This missiles can hit my sage for 25k, everyone except the tank shall be kept almost full health and anybody with less health can be instant killed. Sages have no ability they could cast to heal that much while moving. Furthermore this tend to lag. Many time, we are such as 10m away from the circle when getting the hit. However I found a trick; I'm waiting someone else is targeted to start casting my more powerful but slower heals, otherwise I run and cast quick heals. I also ran it with an operative and had no such issues, the strongest heals they have can be cast while running.
I never (ever) get damage from those red circles, like I said you strafe left or right and keep tapping the space-bar at the same time, it takes 2-3s at most to get out of. As I have also said I have done the fight with my sorc must be about 20+ times and never have a problem healing it either (assuming others are moving out of the circles too). If someone gets hit with the circle and/or bomb combo yes that is un-healable., that's why it's important everyone does not get hit with any damage from the red circles. Do you remember the final boss in the esseles where you had to strafe plus jump out of the purple circles?, same thing applies to this fight.