What would Putin do if he lost the war in Ukraine?

Jake Sullivan, the super-bright US National Security Secretary, believes Ukraine could still win the war, provided they get the $60 billions in military aid from America. Does he really think that's possible or was he just ssying it to encourage the House of Representatives to pass the bill that has already been approved by the Senate, to continue funding Kyiv? More importantly, what does the Biden administration think might happen if Putin loses the war by which I assume that means a total withdrawal of Russian troops and the handing back of all seized territory? That will never happen in my view, but if the victory that Sullivan envisages means Ukraine will survive as a democratic state and will become a member of the western alliance and the European Union, is Putin going to lie down and take that or seek revenge? Defeat for Russia would be seen in Moscow as a massive humiliation, caused not by Kyiv but by the western alliance without whose arms Ukraine would probably never have survived. I think the West would then have every reason to feel concern about what Putin might do. If the diminutive Dmitry Medvedev, deputy chairman of the Security Council of the Russian Federation, had his way, Putin would nuke the West to hell and never mind the consequences. So a victory for Ukraine could have unforseen and dangerous consequences. But clearly there is ittle point in continuing to arm Ukraine unless Kyiv does win some form of victory over Moscow. So there's a Catch-22 here which I don't think Sullivan or the Biden administration or Nato have fully addressed.