After three losing sessions with Pinnacle, two of which seemed alarmingly lopsided, I also had them disable the casino. They had no problems doing it, noting only that is was a permanent ban, and I could not request later to have it turned on. Uhh, no problem.
BTW, my biggest losing streak was not online. It was 21 hands in a row at the Palace Station in Las Vegas. I had actually lost my $2000 buy in around hand 14, but I borrowed money from my friends and played $5 a hand just to see when the streak would end. A week later, I ran $150 into just over $15,000, so I guess anything can and will happen.