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.
That's true because there is no way offline casino will be dependent to online casino, as the matter of fact offline casino will never cease to exist because it works for a serious great purpose for most companies especially for entertainment and is mostly comom in hotel and some shopping centres and people loves playing them because is a kind of keeping themselves well entertained, which is why removing offline casino will never be possible because as new hotel are being constructed that's how they would always consider adding casino in other to serve there customers more better, though online is more better because at your comfort zone you can do it without having to go anywhere plus there numerous betting options.