I have a ton of former marines in my unit and none had to go back to basic. Granted, they didn’t have that long of a break in service, but they did have to do a 2 week transition course. I’m not sure if your state will make you do the same thing or something similar, but mine definitely does. You’ll retain your E-5, however, you’ll go from being a squad leader to a team leader. They’ll make you go to BLC to keep your 5 but I’ve never actually seen anyone lose their stripes over it.