In the modern era it takes a lot to break a country if the people support the government, or even if they just passively don't hate it.

Look at what Nazi Germany and Imperial Japan went through before surrendering. Britain was down to no major allies and was standing alone against a conquered Europe, and in response to Hitler asking for a truce they basically told him to get fucked. North and South Korea were both devastated during the Korean War, but neither actually surrendered anything.

Just in general it's very hard to force a country to surrender through attrition. If you can break them quickly and with overwhelming strength you get things like the fall of France or both Iraq wars, and when the government has no support you get Afghanistan or South Vietnam, but Ukraine isn't seeing any of those issues.

If they begin to lose it will be a slow process and the West will probably just step in with ATACMS, cluster munitions for the 155mm howitzers, F-16s, or whatever else it is Ukraine needs to turn the tide.