Even with the boss clear, all you have to do is start from the first mission and work you way down. By the time you get to the boss again you squad will be around 90-97% HP if you have one "Healing Nodes" and one "Buff Healing nodes" girl in your team.

Its a shame the boss doesnt give more though.
Yesterday I was watching some stuff on Ytube, and kept mindlessly clicking the event, refilling with stamina pots and clicking again. Once I made the full run from the First 10 Stamina map till the Boss map, I reset and did the whole thing again.

Reading the above I suppose I can skip the low stamina missions entirely, and just go with the Last 80 stamina mission listed, since each of those have a set of several submission, that should be plenty to heal up.

Anyway. Love this event. So many Ampys and super Ampys! Since I picked up Kerria from the free 2015 Rainbow Ticket and still need to finish Tarragon and Anewaifu with the Ampies.