I doubt the death of Abe will affect Quad much. Not to mention Abe himself was already semi retired before his death. Quad itself is supported by countries with beef with China, they have common interest to gang up on China. Of course the degree of their hostilities with China and what each country is prepared to confront China is different among each country. But as of now, the cost of them joining Quad is low, and they have no reason to disband Quad or let it fall into irrelevance. You also underestimate the animosity most Japanese right wing politicians and their right wing voters have against China. There are plenty of right winger politicians in japan that are ready to pick up the baton from Abe.