Here’s the video. I did it on Brutal to help show that it will definitely work on Hard.
I’m not even that good of a SC2 player (you’ll see micro mistakes all over the place). So if I can do it, anyone can! Also, I occasionally have trouble playing and talking at the same time, so if I say something weird, call something by the wrong name, or just trail off mid-sentence, I apologize now.
EDIT: I just wanted to add, assuming there’s no randomness to Kerrigan’s appearances:
The initial (start of the mission) Artifact charge up is shorter than the all the rest. It’s ready to go by the 10% mark. All the rest take ~12% to recharge. Kerrigan’s first appears at ~29%. So, that means you can use the Nova to clear/save your base as long as you don’t use it after the 17% mark (maybe 16.5% to be safe).
For example, early in the video, there was hydra/roach/ling push on the left side while I was still building the wall. I used the starting units to repel it, but since it was at about the 10% mark, the Nova could have been used to clear them as well.