effects on brain from nida website:
Alcohol consumption can damage the brain and most body organs. Areas of the brain that are especially vulnerable to alcohol-related damage are the cerebral cortex (largely responsible for our higher brain functions, including problemsolving and decisionmaking), the hippocampus (important for memory and learning), and the cerebellum (important for movement coordination).
in answer to your question: YES, abstinence reverses this damage
I know this both from reading the science and from personal experience; certain things cannot be reversed but those are more rare, and a lot of things take a lot of time to repair
Check out the NIDA website:
Addiction: "Drugs, Brains, and Behavior - The Science of Addiction"
publication from NIAAA:
ALCOHOL'S DAMAGING EFFECTS ON THE BRAIN