Even the most optimistic Russian does not think Russia will ever get beyond https://en.wikipedia.org/wiki/Novorossiya which is not much more than Russia currently occupies. You really think they will eventually march over Ukraine on to Warsaw?? That’s as likely as the exiled Chinese government in Taiwan taking over China.
When the war started, it certainly looked like it. Russian soldiers were in Kyiv at one point:
https://en.wikipedia.org/wiki/Battle_of_Kyiv_(2022)
It was the failure of Russian logistics and the triumph of Ukrainian logistics that beat them back.
Ukraine is keeping Russia where it is at a tremendous expenditure of people and treasure.
Their success in the conflict is not guaranteed.