Rule 611.2b

Some continuous effects generated by the resolution of a spell or ability have durations worded “for as long as . . . .” If the “for as long as” duration never starts, the effect does nothing. Similarly, if that duration ends before the moment the effect would first be applied and doesn’t begin again during that spell or ability’s resolution, the effect does nothing. It doesn’t start and immediately stop again, and it doesn’t last forever. Example: Master Thief has the ability “When this creature enters, gain control of target artifact for as long as you control this creature.” If you lose control of Master Thief before the ability resolves, it does nothing, because its duration—as long as you control Master Thief—was over before the effect began.