Missed the Mime in the prologue. Big deal?

[Talbot]

I'm only maybe an hour past that, worth going back, or no big deal?

[Soulgain]

No big deal. If you need it, fight it once you've finished the game, and then NG+ it just for Mime.

[Talbot]

Does it have any collectibles or anything? Is there other missable prologue stuff I should think about going back for before I get farther?

[Lucyfar]

you just missed one music record, relax, you can get it on NG+ after you beat the game if you care about achievements

iirc it's the Lumiere song

the other missable stuff in the Prologue are the Old Key that let's you access one expedition Journal, one hair cut for Gustave, and i think that's it, the rest are just Color of Lumina and Weapon Upgrade Materials, both you can farm infinitely.