The ease with which they can build such structures would go down. Building while hiding is harder than building while not having to hide.
Having central coordination, for example in the form of a party or some other form of organization, means that strategic goals can be planned for and resources acquired and allocated in a more efficient manner. The previous bigger neonazi party, the NPD, fulfilled that role for quite a while.
Organizations and people are not that interchangeable for these purposes. Workflows, institutional memory, leadership all matter. That's why targeted assassinations of leadership even in cell-like structures can meaningfully disrupt e.g. terrorist organizations' effectiveness. Similar things can be accomplished by simply disrupting business-as-usual.
Didn't they largely leave to join the BSW querfront? I actually don't know the numbers, but at least some of the more prominent RF aligned people left the Left.