If you work for a practice that will let you take patients during breaks and especially in the summer, I would absolutely retain your license. Hygiene brings in excellent money, and there really isn't much else to do in such a short summer unless you want to do research within your school or something like that.
Also, if it's not a huge pain, you should always retain any medical licenses...there's no reason not to, and you'd hate yourself if you needed it and simply let it lapse. Again, it depends on how much coned credit and money you need, but I don't see a reason not to.
It'll be great to have all your fellow classmates drooling over the fact that you get real patients and will rock all the perio stuff 😉