I'd call a redesign successful if it moves the goals it was meant to serve, so I'd set a baseline before launch and measure against it. Brand surveys and recognition tests would show how perception changes, while A/B tests on the website would show behavior, such as ticket sales, event inquiries, and memberships. I'd also test accessibility across real touchpoints and check whether the team can produce on-brand materials more easily. I'd give it six to twelve months, since brand trust builds slowly and a short-term dip is normal.