If the land based casino do not offer the online version of thier casino, they will soon find thier business lacking gamblers because everyone wants to gamble online while being comfortable at home. Those casino who will not have online web based versions will surely die sooner or later.
However this doesn't mean that they completely end the physical setups, it will be better if they run both online and physical casino side by side. Yes, there will be some initial setup cost but this will soon be recovered as casino start to gain online traffic.
I disagree that offline casino without online part is doomed to fail. I have googled Las Vegas popular casino Bellagio and they dont have an option to gamble online. However they are still in the business. That is because offline casino is not only about games, it is about hotel, entertainment, shows and etc. Online gambling is only gambling oriented business, offline gambling offers much more.
You could be right as it is a complete entertainment with hotels, and the the other perks. But as far as I know, even big casinos will have to go online as some point, at least from the casino that has been put up here, in the pandemic, they established somewhat a online presence, but not sure if their online version is still up and running as we all know that we are back to normal again.
But at the end of the day, there could be gamblers who really go to play and not be entertained and stay in such hotels because obviously, it's going to be expensive and we small gamblers play to win money and not to spend it to stay in the hotels.