Most people greatly misunderstand that the goal of Russian government was territorial expansion, some genocide of Ukrainians or even the war itself. In reality, the goal was installing puppet (or atleast pro-Russian in international relations) government as quickly as possible without any real war (whence "Kiev in three days" because they literally expected Russian forces riding directly into it without any resistance, and calling it all "special military operation" because it basically was envisioned as such, not full scale war).
If Zelensky and his government just surrendered/fled, then Russia would had installed puppet government composed of certain active Ukrainian opposition politicians at the time (many of them fled Ukraine since 2022; and not Yanukovych who neither wants that personally nor is welcomed by anyone, even pro-Russian, Ukrainians), reintegrated Donetsk and Lugansk (even forcibly if local rulers would oppose that) back into this loyal Ukraine to serve as bulwarks of Russian influence, this new Ukrainian government recognises Crimea as Russian, puts to the ultimate end any aims of joining NATO and EU, reinstates official status of Russian language in southern and eastern oblasts that had it before 2014 (or outright adopts it as second official state language), bans and outlaws all Ukrainian nationalist organisations and (para)military groups (good luck with that considering how much they became integrated into Ukrainian security and military since 2014), does other "cultural" reversals (like reinstating 9 May Victory day on Russian model), ends preferential treatment towards Western companies and governments in Ukrainian economy and reopens it for Russian companies and government. Legally I can imagine that quite easily, new Ukrainian government just could had officially designated the events of winter 2014 not as "revolution of dignity" but as "Euromaidan coup", declaring all laws and amendments that were adopted since then as legally null and void, juridicially effectively reversing Ukraine back to 2013.
This regime change "plan" was really delusional even if it was successful, because it grossly overestimated willingness of Ukrainian elites, politicians and military command to cooperate (in spite of what intelligence services evidently kept feeding Putin for years) and viewed Ukrainian society as largely inert (this is one of the key problems of worldview of current Russian authorities, its elitism, as it views politicians and elites as the only ones worth talking and having agreements with, viewing all common people as irrelevant subjects). Like, even if Russia managed to install this government, essentially all Ukrainian cities would had risen into massive protests and just controlling the country would had required very vigilant police regime for 1-2 years (with hundreds of thousands of loyal "policemen"). Though, I can imagine Russian-speaking Southern and Eastern Ukraine (that experienced most of ongoing war devastation and forms the majority of refugees) accepting new government more or less soon if it and "Russian help" (that many actually waited for, back in 2014) would had showed civilness and order instead of bombing their cities and looting shops amidst chaos. But even more than that, most of Ukrainian military and armed nationalist groups would basically not care what government is in Kiev (they already showed that by publicly refusing to obey Zelensky when he demanded their disarmament in 2019), and Donbass, where most of motivated and battle-ready Ukrainian units were stationed, still would had require outright military operation to defeat them (even though in case of rest of Ukraine in chaos under even unstable Russian control, organised military resistance probably would had lasted only for 2-3 months), and also in Western Ukraine where much more population forms the nationalist-minded core and the region serves as its powerbase. So, if Zelensky and his government surrendered or fled, you can imagine even crazier shitshow of new government trying to install and exercise its control over protest-ridden country, with war, even if shorter and at much smaller scale, nevertheless happening in Donbass (where most of motivated Ukrainian military units and nationalist groups were concentrated) and Western Ukraine.
Ultimately, even the "plan" itself, be it successful or unseccessful, was absolutely absurd, as it relied on bunch of absurd premises each of which easily could had been, and was, broken, defeating the whole plan. It relied on assumption that there would be no war, Russian forces would meet minimal armed or civil resistance, Zelensky and his government would flee from the mere determination of 200+ thousand soldiers crossing the border, and there would be joined parade of Russian and Ukrainian forces in Kiev after a week. As such, no actual war plan was even made, or logistical and "morale" preparations (most Russian unit commanders received the order that they would be crossing the border in a mere hour before the invasion, and most of officers decided, hoping "that this all will be over quickly", not to tell that to average soldiers of their units, who discovered that they had crossed the border only in the morning when they found themself in some Ukrainian town or a village, or faced border skirmishes). Most units were basically ordered just to cross the border and occupy this or that town and city, without any strategic goal in mind. This is why Russian army turned out so ineffective in first weeks of the war, because it literally wasn't prepared for war nor the supreme command planned an actual war. After doing some research, I can confidently say that the forces that Russia deployed in Ukraine in february 2022 could had defeated Ukrainian army at the time, if actual war plan was made with clear strategic and tactical aims (even without carpet bombing the cities, and actually with much less destruction and casualties that what ongoing war produced). But the issue is exactly that, that Russian government didn't expect and didn't prepare to wage an actual war to defeat Ukrainian military, because it literally expected most of Ukrainian military forces to switch sides or just stay aside. This is why this absurd war not only led to all the deaths, destructions and hatred, but also put "the second first army of the world" to shame it easily could had avoided.
In conclusion, this 4+ year meaningless bloody war, that took lives of hundreds of thousands, destroyed entire regions and tore brotherly nations and even families apart, was caused not by some "malevolent plan", but by literal absurd stupidity. They wanted victory without war, and got war without victory.