If the community died after you left, you failed.
It's misguided to brag the community was fine until you left. Proving this point with data becomes surreal. Worse still, it shows a lack of respect for the community.
If the community died once you left, it means you didn't hire a good replacement, properly train the new community manager, undertake a proper handover to the new community manager, nor put systems in place so the community could sustain and increase its high level of activity.
If you're leaving, you owe it to the community (and your future career efforts) to ensure the community thrives without you.
You need to be actively engaged in finding your replacement (tip: hiring someone from the community usually works well). You need to properly train them in community management and in the unique aspects of your community. Ideally, you want to work side-by-side with the new community manager for a few weks.
You want to give them the best possible handover. This handover announces the new community manager in the best possible terms. It includes introducing the community manager to all the key members. It means interviewing the new community manager and ensuring they post threads asking for ideas about what they want in the community.
Would you rather point to a community that's thriving since you left or one that's dying since you left?