I just hope it helps you.Your island really shouldn't be that hard to remodel. Just be sure to keep the mesh as straight as possible. I've posted a few screenshots here so you can see what I'm referring to.
The first 2 are of Yedahna, which you can download via drizzle. It's a bit hard to see, but the meshes overlap by 1 face.
The second 2 are of Rehahts, an age that's still in development. Rather than just have 1 mesh blending into another, it has a single mesh that blends into 2 others.
Something to keep in mind if you decide to use blends, is I've found they don't play well with lightmaps. In Yedahna, the multiple UVTextures combined with Vertex paint - caused a bad flicker along the edges where the meshes were blended. To get around this, I had to create a large custom texture with the lightmap on it. That way, the mesh only had a single UVTexture. It's not a very graceful fix, but as you can see - it worked out rather well.
Just something you might choose to keep in mind.
