لَا مَحَلَّ لَهَا مِنَ الْإِعْرَابِ
The clause occupies no external syntactic case position.
If the first sentence is an independent opening or resumption with no external case position, a second sentence cannot share that nonexistent position. One must instead ask whether their meanings or predications should be placed under a common connective relation.
Thus lack of syntactic position does not automatically prohibit all joining. It shifts the inquiry from grammatical co-function to semantic coordination, preparing the later classification of cases in which separation is required.