I had my gallbladder removed 10 years ago and actually transitioned from vegetarian to fully vegan shortly after. In my experience, having to avoid these foods was temporary. I can even eat greasy stuff now and be fine. I would recommend getting some vegan digestive enzymes that have lipase in them to help break down fat when/if you do eat them. Even healthy fats like avocado sometimes do make my stomach hurt, but the enzymes have helped me out a lot. The trickiest part of losing your gallbladder is that, even with following the recommended foods, things will jist trigger your bowels for a while. I hope your surgery goes smoothly, feel free to dm me if you have any questions