You are wrong. Ukraine did exist as a separate country. Indeed, for several centuries it was the center of Rus civilization. You might as well argue that Poland never existed as a separate country.
Ukraine became a part of the Russian Empire under Peter the Great, much like Scotland became part of the UK. It was not absorbed, it was attached.
Ukraine was never called Novorossiya. That is like saying that South Dakota was once called the Black Hills. Novorossiya is a separately defined area within the Ukraine, which was liberated from the Turks.
Again, like Scotland and the UK, it is not correct to look at Ukraine as a former Russian (as now defined) possession. During the time of the tzars, Ukrainians made up a good portion of the ruling elite of the Empire, but Ukraine maintained a separate identity within the Empire.
If you go to Wales, you will discover that the Welsh language appears first on signage. Should the English immigrants revolt? Indeed, should those who only speak Spanish in the SW revolt at the idea of English being an official language?
In other words, Russia started from there.
The toponym Ukraine means frontier, borderland of Rus.