"I don't think we'll get back," Severus answered, perhaps a bit more honestly than he should have. "However we got here, whatever we're doing here, we've been removed from our universe. These futures that we're supposed to have - that people remember us having - are rewriting themselves. At least, I think that's how it works."
Severus had theories upon theories concerning the type of theoretical time travel they had accomplished. There were so many bad things which could happen, which was precisely why their universe tightly controlled time travel through time turners the way they did.