Here's a weird one. What if you have a monster with "Strengthen", during battle a friendly monster gets down to one health, then your monster with "Stregthen" dies? It was giving +1 health to the monster that only has 1 health left, does that monster die or stay alive?
Answer is stay alive.
Example battle - https://splinterlands.com/?p=battle&id=sm_7iNfWXPbGT73DhyydmZT
Happy battling!