They'd have to fly like that the whole way from Ukraine. I have...doubts. You could be right. Which case, the Russians are going to have to reposition a LOT of AD units or the Flying Cosacks are going to wreck havoc on the border.
No other country aside from Ukraine is going to attack Russia. That would be a nuclear war. Russia has to treat this war as though its survival is at stake, and indeed in many ways it is once it did launch it, because the West will try to thoroughly destabilize Russia and attempt to place pro Western compradors in power and probably even foment civil war within Russia if it does lose - that is give up without actually having Ukraine neutral, secured all the Donbass, and clearly demonstrated the ability to inflict highly damaging punitive actions against attempted Ukrainian counter offensives and especially strikes in Russian territory and able to repel easily any Ukrainian counter offensives in the South along the Crimean corridor.
That means it has to accelerate the pace of the Donbass theatre and undertake much strategic bombing in coordination with combined arms of various grounds and close air support assault against Ukrainian troops formations there. Look, the Ukrainians are not leaving the cities in the Donbass unless they are thoroughly starved out of them or they are killed. Ukrainian occupied major cities within the Donbass Region are going to be destroyed for the Ukrainians forces within them to leave. The Ukrainians are likely going to use the civilians there as human shields, but whether the Russians opt to do so surgically house by house or go by Grozny style bombardment, there is going to be much destruction.
There are no two ways about it. If an enemy in a large urban area is determined to fight and well equipped to fight, taking that urban area won't be easy. The quickest way is an all out combined arms assault by a force that has greater fire power, but there will be lots of casualties among the attackers. Inevitably there will also be lots of civilian casualties as long as they are present there. The slow way is to surround the city and starve it. Does Russia have the time to do it the slow way?