Complex sentence: After a few weeks Freyre returned to India, via Kathmandu and Patna, leaving Desideri in charge of the mission, and the only European missionary in Tibet, at that time.
Split into simpler sentences: After a few weeks Freyre returned to India, via Kathmandu and Patna, leaving Desideri in charge of the mission. He was the only European missionary in Tibet, at that time.