IIRC, Nero was strongly considering giving up on Britannia entirely. Should Boudicca's military success have continued, he'd probably have decided to abandon the island. Of course, that would probably have some pretty adverse effects on him...
I doubt Nero would go through with it. Watling Street, as others have mentioned, would not completely expel the Romans from the island. Though if he does pull out, perhaps his reign, which had already becoming shaky after the events of 59 CE, might end sooner. Nero was already launching treason trials as early as 62 CE IOTL anyway-one might expect with things going even worse for him on the foreign policy front, he might hasten this process. Something like the Pisonian conspiracy may pop up earlier, and perhaps be more successful. Incidentally, in contrast to defeat in Britain, at the same time Gnaeus Domitius Corbulo is experiencing a remarkable run of success in the east against the Parthians, and he'd make an attractive candidate for opposition to rally around. Indeed, IOTL the son in law of Corbulo, Lucius Annius Vinicianus hatched a plot to overthrow Nero in 62 CE. It's not hard to see how such a plot could gain more steam if the situation in Rome gets noticeably worse in 61 and 62.
Regardless, if Nero pulls out of Britain, one thing becomes apparent: The allure of reconquering Britain would likely be enough for a new Roman expedition once a new emperor takes over for him. It has all the components: the important resource value of Britain, righting Nero's wrongs for abandoning the island, and providing a new military triumph against non-Romans to inaugurate the new regime.
Augustus gave up Germany after Teutoberg, and was content with a nominal submission from the Parthians after Crassus' and Antony's failed expeditions. And indeed, post-Augustan Romans didn't do much expansion compared to their forebears. Whilst "Romans don't accept defeat" is arguably true of the Republican period, by the first century there seems to have been a growing realisation that the Empire was reaching the limits of what it could realistically conquer, and I'd expect a major defeat at Boudicca's hands to be seen as a sign that Britain was too distant to keep control of. Most likely there'd be a punitive expedition or two with some nominal submission from the southern British leaders, but no meaningful direct rule.
Rome was in a uniquely weak military situation following Teutoberg that they were not in during Boudicca's rebellion. What made the rebellion even feasible-the Illyrian Revolt-is also what made Rome practically unable to respond to the loss of 3 legions there. The Roman military was stretched perilously thin by the time Teutoberg happened, and would need some time to recover. Augustus could not really afford to expend the men and resources to retake Germania even if he wanted.