What would happen to NPFH should it sever ties with ADL?

Essentially, nothing.

NPFH chapters would have to change their names since NPFH is a registered federal trademark of the ADL. NPFH chapters would then simply continue their good work under a different name. The structure, membership, general goals, and activities of NPFH would remain the same as they are now. But, again, NPFH cannot continue to be sponsored by an organization whose policies and actions are incompatible with human rights and the stated mission of NPFH.