Figurative expression for outrageous/unlikely/overly bold claim

Question

What expressions could one use to qualify an expression as unlikely, to soften the impact by changing it from accusation or hyperbole into unlikely (if outrageous) conjecture? Something like "God forbid" but more neutral, with no deities involved?

• Assuming he knows something about the criminal case, or, ......... he's the murderer?
• That was a small event, but with enough coincidences, this could ......... lead to war!
• Watch out for your daughter, she might marry not just someone of lower stance, but a foreigner an outright commoner, or even ............ a godless Negro!

Answer 1

I'm not sure there's enough information in the question to give a worthwhile answer, but here goes...

even fits in all cases (except the last, where you've already got it)
Heaven forfend! doesn't mention a deity and has a comically archaic ring to it
horrors! might be too "1930s England"
worst of all is at least literal
worst-case is a modern colloquial update of that

Answer 2

I favor "perish the thought." It has a close idiomatic structure and meaning to "god forbid."

Answer 3

What about hopefully not?

That was a small event, but with enough coincidences, this could hopefully not lead to war!

Answer 4

At worst seems to fit in all your examples.

• Assuming he knows something about the criminal case, or, at worst he's the murderer?
• That was a small event, but with enough coincidences, this could at worst lead to war!
• Watch out for your daughter, she might marry not just someone of lower stance, but a foreigner an outright commoner, or even at worst a godless Negro!