If it is only for the summer vacation (let say 4 months) you will only have to inform one of your superiors. You may be asked to fill in an extended leave without pay permission to be approved by the CO but usually not for the summer and for sure you will not have to quit the reserves.
Also if your MOC requires you a high level of security and you visit the so called scheduled countries you may have to pass a brefing when you leave and will be asked a couple questions when you are back (you will need to provide a lot of info such as dates, addresses, names of all places/people you have visited).