The 30% ruling is granted to you when certain criteria are met. When granted, then you can use the ruling for the period set in the ruling certificate. However, not every employee stays with one employer for the full period of the 30% ruling, hence it is possible to change from one employer to the other. But there are conditions to be met, one of them is the three months period.
Between jobs you cannot be unemployed for a longer period than three months. If you are, you lose the right to the 30% ruling for ever. The three months is a result of the expertise a 30% ruling holder has. This expertise is so special, that the rule makers could not imagine such a period being unemployed for a longer period than three months.
So what happens if you take up a sabbatical for a period exceeding the three months. That is not work, hence you are not unemployed? Or if you would like to take get your MBA between jobs or do another education full time, are you then regarded being unemployed?
It has been decided that you are indeed not unemployed, but neither can you qualify for the 30% ruling anymore, as you are no longer regarded being an employee attracted from abroad by a Dutch resident employer. You are than regarded locally recruited, and locally recruited employees do not qualify for the 30% ruling.