People with full androgen insensitivity syndrome (never responding to androgens produced by gonads) or gonadal dysgenesis of various stripes (gonads fail to develop properly and don't make any hormones) usually wind up more or less externally normally female regardless of the state of their sex-associated karyotypes/genoypes (with the internal plumbing variable depending on the exact reasons for lack of creation of sex hormones). In this way, the pre-pubescent female state is probably the closest thing we have to a default inasmuch as that means anything.

These people do, however, fail to naturally go through most of puberty (a few androgens are usually made by the adrenal glands in everyone regardless of sex but not much) which is an active switch being thrown regardless of sex. As such, the secondary female sex characteristics of sexual maturity are not exactly 'default' themselves in the same way.