As you may recall from the stories last year, Fr. Zigrang simply started saying the Latin Mass. He never "went" anywhere until he was kicked out by the bishop. So he never left or disobeyed or became a wandering priest or any such thing, but simply began to say the traditional Catholic Mass of all time, the one that was guaranteed to all Catholics for all future perpetuity of time. That was when the bishop tossed him out.
For a diocesean priest to go off to work with the SSPX without the blessing of his Bishop is for him to become a "wandering priest", since he is acting without canonical power and outside the diocesean structure.
The punishment for saying Latin masses was for direct disobedience to an order from his ecclesiastic superior, when said superior had already been very lenient to the extent that he felt he could at that time in indulging his desire to say the Latin Mass.
Perhaps, had Fr. Zigrang obeyed his Bishop, he would have gained enough trust in time to receive a situation like Mater Ecclesiae or St. Boniface. He didn't have such patience, and we'll never know what the Bishop might have done, only how he did respond to Fr.'s disobedience.