I have time today to comment on either this or the Israel-UAE deal, but not both. So I will pick this, because I'm a bit more likely to say something that hasn't already been covered by others:
This is indeed the biggest challenge so far to Lukashenko's regime.
Whether it falls or not depends in large part on whether the military, police, and security forces turn against him. If they do, he's probably finished. If not, he can probably stay in power. Past experience in such situations (Ukraine, Egypt, etc.) shows that these things can often shift very quickly. There are already reports that some police refused to repress protestors in various cities. If that spreads, the regime will likely fall. Interestingly, they did NOT suppress the very large opposition demonstration that happened in Minsk today.
As is often the case, it's hard to say how much popular support the regime and the opposition really have. Belarus doesn't have neutral public opinion polling. Often, who wins will in part be determined by perceptions of who has the most support, as much as the reality. For a great discussion of these kinds of dynamics, see Timur Kuran's classic book on "preference falsification," Private Truths, Public Lies."
If Lukashenko seems likely to fall, he could potentially be saved by Russian military intervention. But a full-blown intervention would make Putin even more of an international pariah than is already the case. On the other hand, Putin might think it's worth the cost, for reasons described below. Putin could instead opt to send in the "little green men," while maintaining deniability. But there might not be a way to save Lukashenko without making Russia's role very obvious.
In recent weeks, Lukashenko has actually posed as a defender of Belarusian national interests against Russia. But in the last few days, he has tried to make up with Putin, and Russia is one of the very few countries to recognize the legitimacy of his pretty obviously rigged election victory. Putin may not like Lukashenko anymore. But he clearly prefers the devil he knows to another "color revolution" on Russia's border, at a time when Putin himself is facing increasing public opposition at home.
Even more than Ukraine, Belarus is the country most culturally and linguistically similar to Russia. Russian is by far the dominant language of both business and everyday life in Belarus, and there is relatively little history of Belarusian nationalism as distinct from the Russian kind (very different in that respect from the Ukrainian case). Thus, the example effect of Lukashenko's fall (if he falls) might be great. Note that most of the protest signs in the Vox article above are actually in Russian or (in some cases) English rather than Belarusian (a language very few people actually use).
In "normal" times, the eyes of the world would be upon this crisis. But thanks to Covid-19, the Israel-UAE deal, and other developments competing for headline space, many fewer people in the West are paying attention. We also have a US president who couldn't care less about democracy and human rights, and wants to stay on Putin's good side. All of this tends to work to Lukashenko and Putin's advantage, unfortunately.
If I had to guess, I would say Lukashenko is more likely to stay in power than fall. I think the combined backing of Putin and (most) of his own security forces will see him through. But I could very easily be wrong about that, and I hope I am!