Darryl,
I may be completely wrong.. So grain of salt time..
But as I read the rules.. If some one sails in an event that is of international in scope and is outside the ISAF then all sailors (skipper and crews) will lose their ISAF membership and thus could be protested from any sanctioned International event.. (NOTE protested by either a competitor or the organising committee)..

Losing ones ISAF membership doesnt automatically lose ones national sailing membership.. However losing ones national membership automatically cancels ones ISAF membership..

Losing ones National membership doesnt lose ones state membership.. One may lose their state membership and still sail with their club..

Membership starts at club level.. Part of the fees include monies for all membership levels.. So joining an affiliated club after an event grants membership to all levels of sailing..

The only way I know of where a sailor can be banned for a period from all sailing events is by becoming a person of ill repute.. Have only heard of one such event and Im not sure of the charges or length of banning..