It's easy to look at the side of a war of attrition where you have more information and say that they're losing because you don't have as much information on the other side. Russia has every reason to present itself as still having massive reserves to call upon because it helps their case.

Many people thought that Germany was on the cusp of winning WWI during the spring offensive in 1918.

That being said I think Ukraine's situation isn't great. I was surprised at the seeming depth of the Russia's reserves. They have been sustaining incredible losses for the last year almost, and yet continue to advance. During previous phases of the war we saw them overextend themselves and then have to retreat against Ukrainian advances.

Russia's reserves are finite both in terms of manpower and equipment. They are demonstrating strain in both categories and will presumably start to have sustainment issues soon. If Ukraine can hold together and stop the advance then presumably the next phase would be a negotiated peace hopefully. There's always a chance that some shoe could drop though. Putin could die or get overthrown, the west could withdraw all support, China could start providing blank-check support to Russia, Russia could successfully go into full-mobilization mode.