A lot depends on when the sanctions start biting Russia. If they don't bite at all, or take too late (Nov-Dec), Russia will have some opportunities to try and consolidate some of their gains and hold defensive positions behind geographic barriers.
In my opinion, Ukraine's chance is now. The longer this drags on, the more it'll keep debilitating their economy. They have the momentum now, and UA counteroffensives are already tasting a lot of success. But repelling Russia from every area taken after 23rd Feb will take a lot more arms, and the US has to keep supporting them with arms. 90 howitzers can influence the result on a single battlefield, but certainly not everywhere. Much more is needed. It remains to be seen how the lend lease will work, how swiftly, and how the 40 billion will be disbursed. Hoping to see more heavy arms delivered, and in substantial quantities.
If the supply keeps coming in, UA is surely looking at good times, but pushing the Russians out of LPR/DPR/Crimea might just be over the tipping point of possibility, not least because of how deeply militarized those regions have become, and the public sentiments therein. It might also be a bit too much for any Russian government to accept.