I don't really like the imagery of 'returning to the catacombs' for trads -- sneaking around, saying private masses. There's a kind of romanticism attached to that, and it's endemic among "conservatives", but that's because many of them have mind-screwed themselves out of even fantasies of victory. Dreaming of the restoration of the faith in all its glory, its enemies scattered? How prideful. (No more prideful than the Second Coming, but still.)
As for me: if I'm going to dramatize and fantasize, I will dream of chasing leftists and their sycophants out of the Churches. Let the traditional mass be the only mass you can say in the great cathedrals. Call it unrealistic, but if we're going to fantasize, let's fantasize about the future we want, not the future we'll endure.
You'd think this would involve fantasizing about forcing the anti-trads "into the catacombs", but that doesn't work. Not because it's undesirable, but because it wouldn't happen: if some kind of internal Catholic Reconquista takes place and the Novus Ordo is wiped out of the Church, the reaction of leftists won't be to scurry into the shadows to, fearfully but prayerfully, continue to say the mass they love.
They're just going to shrug and leave the faith behind. Or start saying the Latin mass while working to bring it down again from the inside -- somehow, some way. Perhaps using more novel means.
But for most of them, suffering is not what they've signed up for. They wanted to be part of stamping out their political enemies, and if that's not possible, the fun is gone and they'll go do something else, freed of the need to keep up appearances. You already see something akin to this in the Churches where their victory has been a bit more complete: the Anglicans, the Episcopalians, etc. With no more enemies left to stand against, the reformers leave it all behind anyway. You only need a skeleton crew to slide on the Anglican skin-suit and, say, argue that their increasingly vague and non-committal Christian faith demands blessing polyamorous lesbian trans sexual unions.
We'd see the same if vanquishing their enemies wasn't even an option anymore. And so, that's the future we should work towards.