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It’s hard to paraphrase all that, the short of it is that there were no alternatives, not at that point.
The Allied chiefs knew well that their failure to make an alliance with Russia would mean the destruction of Poland. There was no other conceivable hope of preventing Poland’s liquidation
My arguments are the same as those laid out in the first comment by AES_Enjoyer, as are those of Denna.
Importantly, you never stated what those “several alternatives” are.