What grosses was the OP looking at? I'm looking at w/e 9/11 and they made almost a million dollars, and was 5th highest grossing of the week. Considering post-Labor Day is when most grosses drop precipitously, which most every other show did even with the Broadway Week promotion (and Cats didn't need to participate in) the fact that Cats did so well only proves it can sustain itself through the holidays, if not further.
(And let's face it, most people don't even care about Leona, or or in the US even remembers who she is anyway, so I don't see her leaving as having any effect on grosses.)
"Hey little girls, look at all the men in shiny shirts and no wives!" - Jackie Hoffman, Xanadu, 19 Feb 2008