I recently asked this related question about animating a solid mesh into smoke, and a solution that I might use is to shroud the mesh in smoke heavily whilst the mesh animates to zero opacity, which sounded simple, except there's a problem:
The mesh owns the smoke, and mixing it's material with a transparent shader hides both the mesh and the smoke.
How can I hide the mesh without hiding the smoke also?
One solution that I thought of could be to create a duplicate of the mesh to contain the smoke that is set not to show the smoke emitter, and then as I hide the mesh that is shown, the emitter will remain but the smoke will continue. This would work, but it's a work-around (noob-ish) way to handle it.