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.