There was a serious proposal for the partition of Russia: the Lenin-Bullitt agreement.
https://www.alternatehistory.com/fo...enin-bullitt-agreeement-of-march-1919.356184/
However, even if the Entente had agreed to it, it would not have led to "two Russias, one Soviet and one Imperial" for two reasons:
(1) It would not have lasted. See my quote from Richard Debo in the above post. ("The Bolsheviks were, in fact, offering a great deal for peace, but not nearly as much as it might first appear. Their proposal was a document of political genius, yet one more example of the 'rotten compromise' for which Lenin was so justly famous. It might just as well have been headed 'A Charter to Bolshevize Russia.' Adoption, in whole or in part, would almost surely have led to the collapse of the anti-Soviet governments even more rapidly than was actually to take place. No one, least of all themselves, believed that they could long exist without foreign assistance. The proposed agreement purported to secure them against the Soviet government and the Red Army. Even if it had, nothing protected them from the Bolshevik party, deeply rooted and active, in all the territories of the former Russian empire. Invigorated by the proposed amnesty, reinforced by added cadres from Soviet Russia, and aided by the instant demoralization which would have swept through the anti-Bolshevik forces once the Soviet government had received some form of Allied recognition, local Bolshevik organizations would have made fast work of the bogus regimes they confronted. When the inevitable came, it would fall well within the agreement for, of course, it provided that no existing de facto governments were to be altered until such time as the peoples inhabiting their territories 'shall themselves determine to change their governments.' This was self-determination Bolshevik-style with a vengeance.."
http://books.google.com/books?id=gQfUB0CXBO4C&pg=PA48)
(2) Even if there is a long-term partition between a Red Russia and a White one, why assume the White one would be monarchist? As I wrote here a few months ago:
"One thing that a lot of people don't seem to understand is that as of 1917-18 monarchism was not very popular among even anti-Bolshevik Russians. Indeed, it was precisely the murder of the Imperial Family that made them heroes to the Whites; a
living Nicholas Romanov would probably be more of an embarrassment than a blessing to them. (BTW, to show how out of touch the Imperial Family was about current politics, their greatest fear was that Nicholas would be coerced by the Bolsheviks into approving Brest-Litovsk!)
"The fact is that not a single White government during the Russian Civil War ever proclaimed restoration of the monarchy as a political objective. (Their official position was always that the form of government of a future Russia would have to be decided by a Constituent Assembly.) "In the civil war none of the White leaders, whatever their private views, called for the restoration of the monarchy because they knew that to do so would be to jeopardize public support for their cause."
https://books.google.com/books?id=CDMVMqDvp4QC&pg=PA28
""As Denikin wrote in one of his letters, 'if I raise the republican flag, I lose half my volunteers, and if I raise the monarchist flag I lose the other half. But we have to save Russia.' For this reason the army's slogan was not any specific form of government, but 'Great Russia, one and indivisible.' "
https://books.google.com/books?id=NAZm2EdxKqkC&pg=PA209"
https://www.alternatehistory.com/fo...d-to-the-romanovs.454503/page-2#post-17784008