XMind brainstorming software supports export to all kind of graphics formats, including SVG vector images. This option is useful when you want to export the outlines. This option is only available in the commercial version (Pro) and the Free version will not be enough.
You can also find other brainstorming tools with support of .xmind format that can perhaps help you achieve the same xmind to svg conversion.
Open XMIND file Open SVG file