Just as photoshop became another tool to use in a designer's library, so to will it be with image generation (a la Stable Diffusion, DALL-E, etc.). There's no reason to think it'll be any different. Sure, the skillset will shift, learning to design prompts will become important for any designer worth their salt, but the job of designer isn't going away. It'll just be changed, just as photoshop changed it and provided new skills to learn and leverage.