A well tool can include a swellable material, and a degradable material which supports the swellable material, but which degrades in response to contact with a selected fluid in a well. A packer for use in a subterranean well can include a swellable material, and a degradable material which supports the swellable material. A method of unsetting a packer in a subterranean well can include the steps of, after the packer has been set in the well, exposing a degradable material of the packer to a selected fluid, thereby degrading the degradable material, and a seal element of the packer being unsupported by the degradable material in response to the exposing step.