Remarks by Kirill Khlebnikov reproduced in "California Through Russian Eyes" by Gibson, p. 332, say that one defector from Fort Ross had headed to Mexico. Who was the unnamed defector?
The Fort Ross Conservancy published a roster derived from censuses taken at Fort Ross in 1820, 1821, 1836, and 1838. It shows three individuals who may have deserted to Mexico from Fort Ross: Moliavin, Volkov (possibly Terentsii Volkov), and Stepan Kornilov.
A few more details on runaways are in The Khlebnikov Archive. In the 1822 section, Khlebnikov refers to a deserter named Shebalov. In the 1824 section, he names Prokhor Egorov and Rodion Shebanov as authors of another escape attempt, both of whom had at least previously been at Fort Ross.
Deserters are also mentioned in The Visit of the "Rurik" to San Francisco in 1816. Otto Kotzebue acknowledges receipt on his ship of "three Russian deserters from the establishment near Bodega", identified as Ivan [Strogonoff], Yakov, and Grigor.
Since the censuses predate Mexican independence, Sannie Kenton Osborn's annotation of "Mexico?" would refer to the Viceroyalty of New Spain, not the independent nation. It seems unlikely that the men were able to desert from Fort Ross to Mexico City.
These data may not contain the full set of desertions but I predict it's as close to an answer as I'll get.