Mario died from a heart attack in front of Marco.
Not exactly. She had self esteem problems and she was browsing at a department store. Talbot offered her sex in exchange for the dress. The euphoria elevated spirits and then he started to introduce her to other men. Over time, it became an addiction. Then Marco found out and blackmailed her into being his "Madam". The fitness club, I believe, was a front for a whorehouse.
Wasn't one of the major plot points at the end that Reena and Grant had a bet over profits at World Oil, and if Reena lost she had to sleep with Grant, who had just learned that Judith was faking paralysis, so now they were free to be together, but Reena had to chose whether to move to New York and try to start something with Grant?