I don't think Reddit will go extinct (at lest, not for many more years), but I don't think it will federate either, because theyll find it even harder to make bank than they already do, espeially when most of the rest of the fediverse will likely immediately de-federate them as soon as they get a foot in the door.

It will dwindle to insignificance with a few die-hard users, like Yahoo, and eventually fizzle out through lack of funding. Or it will be re-purposed and used for something different, like Myspace, and be quietly successful in its new but much smaller role.