Should a worshipper interrupt his individual prayer and join the congregation if he finds them praying behind him while he is in the first rak'ah?

Scholars have differed concerning an individual who begins a fard (obligatory) prayer alone and then a congregation arrives. The preponderant view is that he should complete two rak'ahs (units of prayer) and then join the congregation, due to the desirability of transitioning from a fard to a nafl (supererogatory) prayer in order to attain the congregation. However, if he fears missing the congregation while he is in the first rak'ah, then it is better for him to break his prayer and join the congregation, because interrupting a fard prayer is permissible here for something more beneficial.