What is the test for rescission in a personal injury case?

[T]here can be no rescission where the rights of third parties would be prejudiced.... 'It is, of course, fundamental that, where the rights of others have intervened and circumstances have so far changed that rescission may not be decreed without injury to those parties and their rights, rescission will be denied and the complaining left to his other remedies.'

Id. at 763, 20 Cal.Rptr. 391 (quoting Beckwith v. Sheldon, 165 Cal. 319, 324, 131 P. 1049 (1913)).