The only reason ESL games were set to be played in the middle of the week is that all ESL teams intend to participate in national leagues. If UEFA do ban them and if the clubs abide this decision, ESL participants won't have any reason to stick to midweek. And it makes situation even more spicy.
ESL will surely move their games to weekends. Also, they will surely spread all of those top games throughout the weekends. It will give them more money from TV contracts and sponsorship deals. And it will destroy all the national leagues because we all know what games most fans will prefer.
With financial backing ESL have, they will easily maintain such a siege for years. UEFA won't endure even two seasons, because unlike ESL consisting of 20 teams max, UEFA will have to financially support tens of leagues and hundreds of clubs. It would be impossible in their golden years, it's beyond impossible in this economy.
So, UEFA are either bluffing (best case scenario for them) or they're not seeing clearly the entire matrix of options ESL have to respond with.