The term you're looking for is internal/inner émigré, although Mary McCarthy (“A Guide to Exiles, Expatriates, and Internal Émigrés”) wouldn't agree with you because Nabokov actually left.

Google "internal émigré" + Nabokov and "inner émigré" + Nabokov.
There are plenty of articles that mention them together.

Or look using Google Books, as there are also many mentions of both the term and this particular author.

There's also an interesting discussion here that explains McCarthy's thoughts on the matter and analyses the term further:
https://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=48...

"Should Nabokov be considered only as an exile during these three very different periods of his emigration? In her essay “A Guide to Exiles, Expatriates, and Internal Émigrés” (1972) Mary McCarthy distinguishes among several categories of émigrés, which include exiles, refugees, expatriates, and internal émigrés. One of the first influential literary figures to insist upon such a distinction, she applies her theory to Nabokov, who was driven away from his country by the totalitarian regime; James Joyce, who willingly abandoned his country due to political disagreements; and Boris Pasternak, who never left the Soviet Union despite being virtually sentenced by the government to life in isolation. Pasternak, who was given an opportunity to leave Russia, refused to become an exile: “I am bound to Russia by my birth, my life, and my work. . . . For me to leave my motherland would be equivalent to death” (Rowland and Rowland 493). McCarthy mentions the supposed jealousy that Nabokov, as an exile, must have felt toward Pasternak, an internal émigré, who despite his hatred for the Soviet regime never left the country. If Pasternak equated exile with death, Nabokov recognized the opportunities that exile offered. In an engaging discussion about this problematical subject, McCarthy proposes how to apply the term exile: “The exile waits for a change of government or the tyrant’s death, which will allow him to come home. If he stops waiting and adapts to the new circumstances, then he is not an exile any more” (Prose 69-70). This particular definition is ambiguous: does it mean that to be considered an exile one must resist any attempts at assimilating into a new culture and spend his or her life rejecting possibilities that the new country has to offer?"

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Note added at 4 hrs (2021-05-25 17:00:42 GMT)
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*analyzes the term further

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Note added at 4 hrs (2021-05-25 17:09:21 GMT)
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Here's something else about other prominent Russian writers:

"Three Inner Emigres: Anna Akhmatova, Osip Mandelshtam, Nikolai Zabolotsky" https://www.jstor.org/stable/126861?seq=1


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Note added at 4 hrs (2021-05-25 17:11:58 GMT)
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"In the introduction to her translation of 15 stories of Yevgeny Zamyatin, “The Dragon” (1967), Mirra Ginsburg recalls that Trotsky, while he was still in Russia, called Zamyatin an “internal emigré.” But Zamayatin became an “external” emigré too, after writing a bold and unrepentant letter to Stalin. Through the intercession of Maxim Gorky, he was allowed to leave in 1931 for Paris, where he died six years later."
https://www.nytimes.com/1972/07/29/archives/one-vote-for-her...

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Note added at 4 hrs (2021-05-25 17:14:09 GMT)
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"We discover Stanislavsky as son, brother and father, as lover and husband, as businessman and "internal emigre." He is seen as a wealthy tourist and an impoverished touring actor, a privileged subject of the Tsar and a harried victim of the Bolsheviks."
https://www.routledge.com/Stanislavsky-A-Life-in-Letters/Sen...