It hasnt been disproven even once. The usual attempts to do so deny geopolitical realities (e.g. assuming the Finland-Russia border is as vulnerable as the Ukraine border).
Georgia was, obviously, left alone after it dropped its NATO ambitions, disproving the rather quaint theory that Putin is intent on reforming the USSR.
And what Kalingrad is to Poland, and what Transnistria is to Moldova, and what Abkhazia and South Ossetia are to Georgia, and what Donetsk, Kherson, Luhansk, Zaporizhzhia, and Crimea are to Ukraine.
If you wish to understand this issue, you must condemn the russian invasions and annexations in Poland, Moldova, Georgia, Ukraine, and many others.
Georgia was, obviously, left alone after it dropped its NATO ambitions, disproving the rather quaint theory that Putin is intent on reforming the USSR.