Thanks to everyone who suggested editing the comments before deleting them, but I decided to just go through the last 3 years of comments and edit them instead (yay, macros).
I could only go back 3 years on the comments in RES, and I'm pretty sure comments to subs that are currently private weren't shown. I was actually looking for a specific comment to archive, but r/TheOrville is private and none of my posts/comments were visible.
The one toward the bottom with 761 points on the post titled "What's the worst adult tempter tantrum you've ever seen or heard about?" was a really good story, too. Maybe I'll share it here, sometime.
They're going to have a very very bad time of that under GDPR