“If Bob Did Not Exist We Would Have to Invent Him” is a comic animated musical. Our narrator, “The Rebel,” hosts a show called, “Master Theatre” in which she regales us with songs, in between segments of the following story: Two drifters, a normal one and a 17 story tall one, meet, form a friendship, go on the road as a comedy team, and then begin, mostly by accident, a series of fake religions. As these things often do, they turn sour, and there is a trial, madness, a military compound, and ultimately an offer of escape to a better planet. The narrator, (who appears in Erin Hayes’ earlier films, as do some of the other supporting characters,) sings us through it all. This movie is based on an unpublished novella, written by the filmmaker.