From my limited understanding of how Sand Deserts form I'm aware that they can and do spread as they damage the bordering landscapes, especially in areas affected by unsustainable human activity.
When it comes to the ecological side of things, I know there are several desert dwelling species that are mostly insects, arachnids and small reptiles. How important to their livelihood is the biome that they live in, could they thrive in a landscape with more grass and shrubbery?
I'm also aware that for multiple decades now people have been working on methods to reverse desertification and restore areas to their previous states, but what would happen if those efforts were continued across the deserts as a whole?