After Boudica burned London Nero seriously considered pulling out of Britain, what would happen if he did. I know Nero's successor would attack again, but how would that effect Rome?
Sounds like the sort of thing that would collapse a regime, or just an afterthought like Hadrian's withdrawals. But the fact an open rebellion was going on would make it seem like the former is most likely.
Nero's regime, already shaky and soon to fall anyway, finally caves in on itself. Actually, it would be quite intriguing if an usurper arises at about the same time along the Rhine legions, and Paulinus in Britain recognizes him as the legitimate emperor-so ignore the orders.