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.