It's even fairly plausible that the utf-8 numerical encoding can be reverse-engineered from a few samples; enough languages' text generally only use characters from few enough blocks to identify. If you're really motivated, you can probably work your way through most of the languages with phonetic writing systems.

But then there's CJK Unified Ideographs, where the characters that get used are scattered essentially randomly because the ordering is only relevant if you already know how many and which characters were encoded at what point in the history of Unicode.

There are large swaths of Unicode which, if somehow totally lost, would essentially require finding font data or character reference tables to recover.