They will be just like any other company attempting to sell their product online. As long as there are at least two competing against each other they will look into all forms of online advertising.
Maybe a good example of what is to come is to follow the UK market. There are land based casinos now that have an online presence and have affiliate programs.
I don’t know why MGM failed before but, branding or not, online businesses need traffic and that will continue to be.
Would it be as profitable as now? That is questionable but entirely dependent on how competitive the situation becomes.
The affiliates that will really get hit here would be older established big money ones that have huge amounts of players on lifetime revenue share. It’s like starting over to them. But if I were them, I’d try and hold onto my sites and keep the rankings in natural search over the next 2-3 years.
If it gets to the point where the US government chooses the sane option of regulation then that will open up paid search again. Some of the affiliates that have been around long enough to remember when this was still available should have a good idea of the money involved there. It may not be what a big affiliate has grown accustomed to on revenue share, but it will still be very lucrative.