A dogs gums can grow back some but it does so slowly.
If your dog has periodontal or gum disease that is eating away at the gums then you need to get the gum disease or periodontal disease treated before it gets too bad.
When the periodontal disease or gum disease progresses too far it can lead to death in the dog if left untreated as the gum disease and periodontal disease can cause infection of the blood.
If you have a dog you should get pet health insurance that can help cover costs of dental problems in dogs as long as the dental problems are not a pre existing condition.
It's best to brush your dogs teeth at least a few times per week or everyday if possible to keep the dogs teeth clean and prevent gum disease and tooth decay in the dog.
Also have a professional tooth cleaning of the dog if possible from a vet to prevent the gum disease or tooth infections.