When it comes to matters involving the Shroud, the Giovanni should be all over it. Their great plan involves them collecting enough souls to power a great working that will drop the Shroud for once and for all. By their reckoning, this will give them total power over the dead, and catapult their Clan to the top: a prospect that should scare the unliving hell out of anyone who's ever had the displeasure of dealing with them.

So if the Shroud is, indeed, in danger of being weakened, the Giovanni will most likely act to weaken it further. Fortunately, they lost a large number of their captive souls when the 6th Great Maelstrom went off, but that's not going to stop them. The Clan will find some way to try it with what they have, or else they'll engineer a way to get as many as they need through some sickening atrocity. And who knows? It might actually work.

The brighter side of this scenario is that the Shroud might be strengthened by somehow reversing the whole deal. But figuring that out would require someone to know the fine details of ages' worth of vampiric Necromancy - something in scant supply amongst wraiths in general. And then they'd have to get the Giovanni to cooperate.

The Tremere are also known to dabble in calling up ghosts, and breaking down the barriers between the worlds of the living and the dead. They are the premier workers of blood magic, and can pull off some spectacular feats when their elders put their minds to something. So if the eldest amongst them were informed that the world was about to be swallowed by the primal darkness, they could very well try and shore up the Shroud.

Of course, they'll want some kind of recompense for their efforts, which could lead to the problem of some ambitious moron bringing it all down because someone wouldn't genuflect convincingly. They could also try to turn the situation to a metaphysical advantage, which has "disaster" writ all over it in glowing, green letters. And then there's the fact that Thaumaturgy has become quite unpredictable of late; The Ritual could make things worse, somehow, or else fail in such a way that they unwittingly bring about the Giovanni's master plan all by themselves...

The real wildcards are the Harbingers of Skulls: lately arrived from the Shadowlands, these incredibly-old kindred have joined the Sabbat, and are intent on taking revenge on an unspecified group of vampires who apparently locked them away, untold ages ago. Their skills in Necromancy rival the Giovanni, and they might well be willing to undercut or stymie that Clan's plans in the process of getting back at them.

So, if push came to shove, there is some possibility that the Harbingers of Skulls could act to repair the Shroud, or shore it up. On the other hand, they may want revenge against that certain group of vampires so badly that they're willing to die to get it, and might actually aid them {behind the scenes, of course} just so the other group gets what it wants - knowing full well that nothing good will come of it.

Or maybe they DO want to bring it all down, or are acting on the behalf of something that wants it down. It supposedly took two of their greatest members working in concert to bring them back across the Shroud, but what if they were helped by something else? Something that wants them to act on its behalf when the right time comes around...?

{And as for the Samedi, the Nagaraja, or any remnants of the True Hand who knew the secrets of the Underworld, there are too few of them to form an effective bulwark against Oblivion, or help its approach on anything more than an individual level. That's not to say that one person can't do a lot of damage - consider Xerxes Jones - but as disparate groups whose combined membership couldn't fill a city bus, their pooled efforts would probably be negligible at best.}