Is neuropathy reversible? Yes. However, it's not as simple and deterministic as reversing, say, high BP with treatment, which pretty much always works.
It depends on the many factors, and frustratingly one of them is simply variation from person to person. Some people, when neuropathy presents, never have any improvement despite getting tight BG control and keeping it. These people are in the worst situation, however for most diabetics getting BG under control will improve peripheral neuropathy, restore sensation, and in some cases resolve completely after consistent good control for months, up to a year. Maintaining control is critical to keeping the neuropathy at bay.
As NutriJoy notes, gastoparesis is caused by neuropathy in the vagus nerve. I don't know of any statistical or study data regarding improvement in gastoparesis with improved control, but it stands to reason that if the peripheral nerves can heal, the vagus nerve should be able to improve too. However, there may be differences that complicate that picture -- I just don't know.
Just bear in mind that nerves, if they recover from neuropathy, do so very gradually. There will be no "Big Bang" sudden restoration of feeling -- or functional digestion -- simply by getting BG in line. You've got to get it under control, and stay on top of it.
Took my peripheral neuropathy a full year to resolve as much as it was going to (which was a lot). Rather than being delightedly surprised that my fingers were feeling properly again after seeing my numbers come down, it was more one of those things where, one day after about 6 months of good control, it occurred to me that I wasn't feeling the numbness, ulnar nerve issues, etc. any more. It was more like, "hey, I'm not constantly noticing that stuff any more".
Then I celebrated with a trip to Baskin Robbins with my kids (really, I did! And a rather large Humalog bolus…)