Have you not seen the amount of corruption DOGE department that is headed by Elon Musk is uncovering from the administration of the US government under Biden? Does that mean that America is not a country if we judge it by your standard of corruption?
Same point I wanted the OP to understand. The degree of corruption of a country can not determine its nonexistent. The worst which can happen is a dissolution of power after heightened security and economic crisis and a mediation by international organizations like experienced in Libya during Gaddafi and such situations, only leads to more instability and proxy wars as well as exploitations of country's resources. At least when one talks from the point of insecurity, it's quite reasonable enough but no matter how bad or worse the security challenges Ukrainian government is facing, it isn't as worse as some middle eastern countries facing carnage for long period of years now, yet they didn't seize to exist. Meaning no amount of corruption whatsoever can bring about scraping a sovereignty nation's existence.
In the case of Ukraine, if it eventually goes out of control, which I don't think will happen, these are the few things most likely to play out. There's the likelihood of Russia annexing more Ukrainian territories such as Luhansk and Donetsk which can be absorbed into Russia if the Russian government gains upper hand just the way it was experienced in Crimea in 2014. Already because Russia is a nuclear power, the international organizations like the NATO are being tactical about their full involvements to avoid further escalations. But since Ukraine is a sovereignty nation, little can be done to forcefully dissolve or intervene heavily by the international organizations.