If a worshiper in congregational prayer passes wind, is he obligated to leave the prayer to renew his ablution, even if he is in the first row and might have to pass in front of other worshipers, or should he complete the prayer and then repeat it afterward?

The obligation upon someone whose ablution (Wudu') is nullified during prayer is to stop the prayer, perform Wudu', and then repeat the prayer. They should exit holding their nose for discretion. It is not permissible for them to complete the prayer while in a state of ritual impurity (hadath). There is no sin upon them for passing in front of the congregants due to the Imam's sutrah and their necessity to do so. It is preferable for them to exit without passing directly in front of the worshipers, if possible.