Well, Judaism never really recovered from the destruction of the Second Temple, but that largely affected the urban class who kept rising up against the Romans and getting slapped down (which, let's be frank here, if my religion's center were razed and I was told to follow some other religion by foreign oppressors like the Romans, I'd be angry for generations, too), not the rural classes; I know that Antonine sources say that Domitian was going to exile the Judaeans for rebellion or something, ethnically cleanse them and split them over the Roman Empire, but that didn't end up going through.
The main reason Judaism seems to have gone extinct, except as half-remembered traditions passed down through later Christian and Muslim denominations in the Levant and the Ethiopian plateau, is that the Roman destruction of the centers of faith slowly eroded the faith's unity and power with the population. Sort of like how the Canaanite cults it evolved from got wiped out. What then seems to have happened is that they mostly converted in fits and starts to Christianity or Islam depending on who was in control of the region over the next few centuries, and the faith never got further than the edge of the Iranian plateau and the Balkans. The main problem seems to have been that it wasn't a proselytizing faith but a highly national one, one tied to ethnic identity through the maternal line, which made it hard to get converts that the Muslims and Christians were picking up in droves. The heterodox branch down in Ethiopia petered out without support, if they'd had some tie to a broader community they would've made it without converting.
So, what they need is a stronger national identity. Something, probably a stress, that'll provide a sense of identity among the core urban faithful, allowing them to keep the farmers in the loop or strengthening the faith's core advantage of national identity.
Honestly? Domitian's asshole scheme probably could've done it. Deport them en masse to the Balkans or the Persian frontier or something, provide an excuse to have lots of troops on the Parthian border in case of a war...it's not implausible from a Roman policy POV, and it would create a national myth that would probably ensure increased dedication to the faith over the generations.
Though, without conversion they're never going to be anything more than a minority.