So a few channels that spring to mind were UltraJman and Mas n Vic, there's also Tatsudoshi but most people know that one.
The former did a few lets plays like IWBTG, Cave Story, Metroid Fusion, and I recall Mega Man 7 being one as well, but those have been gone for many years and aside from a cut down upload of IWBTG they haven't been found anywhere.
The other was a channel called Mas n Vic, which featured a guy from TheZeldaDungeon https://www.youtube.com/channel/UCtldOMW0pKAgMkdq8Z6I2KA
doing small reviews of games like Cybernoid and Wii Sports, that channels been dead and wiped for the better part of a decade. Here's an archive.org link
https://web.archive.org/web/20080705173220/http://www.youtube.com/user/MASnVIC
If anyone knows of these lemme know, or even better if one had links archived but I sincerely doubt these'll turn up, especially that second one.
EDIT: User ClementJ642 also has a few videos that are totally gone, like vlogs, wrestling videos, and a few others, I got a couple backed up to Archive.org and a few people sent some stuff, but plenty is still lost.
There's also the user HarvesterofEyes,who originally covered an assortment of strategy RPGs, so Fire Emblem, Shining Force, Tactics Ogre, even some obscure ones like on the Game Gear. He eventually ended up wiping both his channel and his website SRPGAcademy, and aside from a scant upload of four videos, there's basically no traces left. channel was here