I haven't studied this in nearly enough detail to be sure of what I'm saying, but it is my understanding that we quite possibly ARE wrong about the observable universe's size, simply given the newness of the science saying there is an "observable universe". Newton was wrong about gravity, but mostly in edge cases (pun intended); could Hubble et. al. be wrong about the observable universe's size? Could we find a way to send messages faster than light (there are several theories and only one need work)? Or could we possibly cram more people into the universe than seems possible now due to simulations, building smaller but equivalent brains, or otherwise?

If the answer to ANY of these questions could be less, then we could indeed be wrong about the size observable universe (if observable is defined in terms of light even after we develop FTL communication, travel, or observation, then that's stupid (like the current definition of clinical death) and you can replace "observable universe" with some similar phrase).

Besides, it may in fact be worth considering what happens outside the observable universe. We can make some predictions already, such as similar laws of physics and the continuing existence of anything which we could previously observe but has since passed over the cosmological event horizon. If people eventually become one of the things that passes over this event horizon, I'll still care about them even though my caring can not affect them in any way.

Note again that I don't know much about this, and I may be babbling nonsense for most of these points. But I do know that Hubble may be wrong, that humans keep doing things that they'd previously thought scientifically impossible, and that without an observable universe boundary there are still things which are causally unrelated to you in either direction but that you still may care about.