The "other dialect" may not need a special term for it, since it is the structurally unmarked, frame-of-reference variety which may be taken as defining that which is "normal" in the xenolect as well. But were a term to be needed for the non-xenolectal dialect(s), an appropriate one might be matrilect, making up as it does the matrix in which a xenolect is embedded.
Source: wiktionary
For this reason she classifies Rinkebysvenska as "a xenolect, which relies not on radical restructuring, but on a small but symbolically significant amount of influence from immigrant language(s) to render it identifiably different from standard."
Source: wiktionary
As a xenolect develops, it becomes mimolect, that is, a variety whose external appearance resembles that of another (Stewart, 1989: 263-280).
Source: wiktionary