Outside of archeology we basically know nothing about pre-Roman Britain. We hardly know anything about Roman Britain too and we barely know what happened after the Romans left.
Barring some world ending apocalypse I find it hard to imagine that, even if let's say 1000 times less written material survived the next 2000 years compared to the 2000 that preceded us our descendants would still have several magnitudes more information about our times than we do about 0 BC (especially if we're talking about Britain or pretty much any people in Europe who did not speak Latin or Greek).
Barring some world ending apocalypse I find it hard to imagine that, even if let's say 1000 times less written material survived the next 2000 years compared to the 2000 that preceded us our descendants would still have several magnitudes more information about our times than we do about 0 BC (especially if we're talking about Britain or pretty much any people in Europe who did not speak Latin or Greek).