Perloff said her biggest regret was the failure to sustain A.C.T.’s core acting company. (“The city got too expensive — artists can’t afford to live here anymore.”) But the theater’s thriving acting conservatory remains, and in an era that has seen nonprofit theaters become clearinghouses for jukebox musicals and other commercial trifles from Broadway, she has shored up A.C.T.’s reputation as one of the most principled regional theaters in America.