Like several of the other priests who were deported to the camps by the Gestapo after September 1, 1939, (auxiliary) Bishop Mikal had options. In the first place, he might have bolted when the tanks rolled over the border. There was time, and he had an invitation. Instead, he opted to stay with the parishioners in Wloclawek.
The German troops entered Wloclawek on September 14. At that point, being a German speaker who was in a leadership position, he might have made himself useful to the new master; he might have collaborated. From what little I have read of him, it does not seem to have occurred to him. He immediately registered protests about the edicts issued by the occupying forces. He complied with the order to preach only in German, but no doubt said in their language much the same as what he would have said in his own.
The Nazis must have been busy. They took until November 7 to arrest him. He spent a year of so in house-arrest in a Salesian monastery, far from the worst way to spend 1940. The Holy See tried to spring him, but to no avail. Instead, he went to the resettlement and POW camp at Inowroclaw. Again, not the worst place to be, but he suffered wounds on the ears and legs from the torture he received there.
On April 25, 1941, he became Prisoner Number 24544 at Dachau. Typhus spread quickly among the weakened prisoners. In spite of all the other abuse he had received, he was still sent to an infirmary with his cousin, who survived and offered an account of Mikal's final days. In the infirmary, a group of doctors examined him. One said, "Now is the easiest way to eternity." They inserted a hypodermic needle in his right arm; he died a few minutes later. Several days after that, his remains were cremated amidst the steady stream of victims at Dachau.
I know I've made the points before, but I think they are worth bearing in mind. Some folks went because they had to; others, because they had a duty to serve others who went. Some lived in protest rather than fleeing in desperation. They might not have lived as long, but their protest continues every time we repeat their stories.