An analogy I use with my customers is a gas leak in the system is like having a slow puncture in your tyre, you either have the puncture repaired or buy a new tyre, so unless the Engineer carries out a leak test ( either by using an electronic leak detector or pressure testing with nitrogen ) and can locate the leak, and if it can be accessed for repair or a part replacement, then yes if it just regassed then it will leak out again, but no time scale can advised without knowing how big the leak is and how long it will last before you are back to square one.