The adulterer will end up marrying an adulteress or an idol worshiper, and the adulteress will end up marrying an adulterer or an idol worshiper. This is prohibited for the believers.
الزّانى لا يَنكِحُ إِلّا زانِيَةً أَو مُشرِكَةً وَالزّانِيَةُ لا يَنكِحُها إِلّا زانٍ أَو مُشرِكٌ وَحُرِّمَ ذٰلِكَ عَلَى المُؤمِنينَ
azzaanee laa yankihu illaa zaaniyatan aw mushrikatanw wazzaaniyatu laa yankihuhaaa illaa zaanin aw mushrik; wa hurrima zaalika ‘alal mu’mineen