Very likely; your chances are 100 percent. The question you should be asking, though, is how long you would have to wait for one. I'm not sure but I would guess somewhere in the 60-90 minute range.
Other alternatives for creative Mexican cuisine near downtown, but that accept reservations, include Topolobampo (Rick Bayless's other restaurant, next door to Frontera Grill); Salpicon, in Old Town; and Adobo Grill, two locations in Old Town and Wicker Park. You can make reservations for all of these on opentable.com