That, more or less, would be my guess. In this case, the circuit can't be complete because the destination is impossible to reach and the mage either isn't able to cast the teleport spell altogether or feels the flow of magic and knows that if he would attempt to teleport, he would probably appear a few miles above the Isle, in gory pieces. 1) There is no end game summary to this quest and that's for sure - there simply is no such ending in the game audio files. 2) I recall rroyo either adding or at least discussing adding a custom continuation to this quest in A:WIP and/or such a continuation existing in chrisbeddoes' Polished Carcanum. People making those mods knew what they were doing and they surely checked everything before attempting to add to the game something that could be there already.