Menzel's last stop on her tour is the Hollywood Bowl in October. If/Then starts the tour at the Pantages in December. Signs point to her doing the show in LA after a short rest period.
A show like If/Then would seem risky at some tour stops, without Irina, but not at all. Here in Cleveland, we have a subscriber base of about 30,000 people currently (as of last Spring, the largest Byway subscriber base in the country...) The 7 or so shows each year generally run two weeks in a 2,800 seat house = 70% of the tickets for a two week run of this show/any shoo would already be sold before any groups or non-subscribers have even had a chance to buy. Add in big business in cities where Idina does play - and good business in other major markets with big subscriber bases (Denver, St. Louis, etc...) and it may not be stretch to think this show does OK.