Belarus & Russia signed the agreement creating the Union State nearly 25 years ago now, & nothing much has ever come of it. Lukashenko is never gonna relinquish power in Belarus so long as he's alive & everybody knows that. The current quibbling is about oil rates & niggling trade disputes that have always cropped up from time to time.
And Russia is not gonna invade Belarus. Belarus is one of their closest allies, & Belarusians appreciate Russia for allowing them visa-free travel & work inside Russia (Belarus doesn't have a market economy so this is a critical economic lifeline) & the free educations that Belarusians are granted at Russian universities.
Lukashenko is in the worst position he's been in, although he's still trying to rig the election. And he has COVID-19. And Putin could probably use a win.
Should the West Be Worried About Belarus? One can anticipate the announcement of the official results of the rigged August 9 presidential elections triggering a wave of protest, which the Kremlin could exploit and augment if it were prepared and inclined to do so. In Ukraine in 2014, the hapless Yanukovych had even helped lay the groundwork for his country’s dismemberment. Too busy lining his own pockets to pay much attention to tertiary considerations like national security, Yanukovych had allowed Russia over the years to honeycomb the Ukrainian military and special services with its agents, crippling Ukraine’s ability to counter Russia’s bold moves during the “Russian spring” of 2014. By all accounts, Lukashenka runs a much tighter ship than the Ukrainian ex-autocrat, so any Kremlin-orchestrated attempt to create a “Russian summer” in Belarus would have to weigh carefully the possibilities for peeling off local elites or subverting the military and security forces. As in Ukraine in 2014, Russia has troops on the ground already, and it would not be difficult to slip additional forces into the country across a largely open land border. The massive snap military exercises that Putin ordered last week might have nothing to do with Belarus—but they sure would make a nice cover to preposition troops and materiel for possible deployment there. Regarding the attitude of the local populace, the Belarusian reputation for passivity and Russophilia would give the Kremlin grounds for optimism—but could also lead to serious miscalculation, as with Novorossiya.