God forbid that.../ Is my sentence and interpretation correct. Experts, help!

[Alexandro]

Hi

I already know that when you say: 'God forbid that...' that you don't want something to happen.

I was just watching The Tudors on BBC2. King Henry, or rather the actor said: 'God forbid that his abominable plan to assassinate me should have succeeded.' (meaning: Very good that he didn't succeed in killing me.)

Can you use 'should have + past participle' in this sense. I heard it being used like that.

What do you think?
Thanks
Alexandro
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'Everyone can mistakes! After all, nobody's perfect.'

[Dozy]

The sentence sounds OK to me.

[Alexandro]

Thanks Dozy, as usual, but could you also have a look at my 9/11 sentence, please. You know how much I value your opinion. Thanks.
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'Everyone can mistakes! After all, nobody's perfect.'