Merge Voronoi cells boundaries

To recreate the cells, you may try creating TSplineSurfaces from Lines, extract the Faces, extract the Edges, get the Edge Curve Geometry and then create a PolyCurve by joined curves, but it’s quite a convoluted way.

I would use Dynamo to export the geometry in Rhino and create the Voronoi there as it is a more developed environment to play with geometry.