Wither Boss can't heal himself like Java.

Thank you for your report!
However, this issue has been closed as Invalid.

We're already working on achieving parity across versions where possible, and we're very keen to hear your requests or suggestions, so we'd encourage you to make a post at https://feedback.minecraft.net, or upvote an existing topic there.

If you're not sure whether your issue is a parity request or a bug, hopefully this article will help explain further: Parity Request Guide

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