I haven't found a reasonable way to recycle shoes and heels yet, but you can resell them on a specialized site.
If your shoes need maintenance, don't hesitate to take them to your shoemaker. Please explain that the heels come off, but the shoes can be maintained. You will find here more specific information on shoe care.
We've also created videos that teach you how to transform your current heels. It's a great way to breathe new life into something you don't wear as much or are worn out.
Thanks to awesome customer @mpastinelli for creating these tutorials.