You can learn to control the foods you eat, and how to eat, to avoid a lot of the gas. Many people can still burp after the surgery, but vomiting should be avoided. There are antinausea meds that do a good job.
I am getting good relief from gas just by not eating bread and taking cheap, generic pancreatic enzymes (Pancreliapse 5000 $17, including shipping, for 3/day 3 months supply by mail order from my pharmacy). I have NO gas problems! Food is digesting much better!! Abdominal pain is so much lower!!!
Make sure to cooperate and do all the tests! It's incredibly important that the docs get all the right figures: how long your esophagus is, how well you swallow. They have to determine how tight to make the wrap and if they can drop the esophagus into the abdomen enough to avoid having to make a neo-esophagus.
Also make sure you are at a really good hospital with a surgeon who has done thousands, not just hundreds of these operations. It IS major surgery, not to be taken lightly.