Mary Louise Wilson, who won a Tony for her turn as Big Edie Beale in “Grey Gardens,” departs the Broadway tuner July 29.Lead actress Christine Ebersole, who also picked up a Tony earlier this month, plans to continue in the show at least until her contract is up in the fall. A London incarnation of the musical, toplined by Ebersole, is in the works. Doubts about the longevity of the Rialto production of “Gardens” have been fueled by the show’s often modest sales, but recently the tuner has gotten a post-Tony boost. For the week ending June 24, receipts were up to $465,615. Both Ebersole and Wilson have been attached to “Gardens” since its first workshop at Sundance in 2004. A replacement for Wilson has not yet been set.