I've solo healed garuda ex, I could probably manage Levi ex if I could stay on the platform (I use gamepad, the only time it's a hindrance for me is I have trouble turning the cam quick enough combined with aus latency I tend not to be able to dodge when he dives over the arena).

I've had to solo heal titan hm and CT/ST more times than I can count thanks to the amount of people that go in as sch just for the quick queue times then proceed to run TOWARD aoe/edges so they can die and get a carry for the fight. I've had to heal T1 when the other healer has dc'd, think the same for t4.