Missed anatomy is the most frequent cause of apical development. In first upper molars definitely MB2 is mostly missed canal. Both approaches surgical and non surgical can be applied to solve this kind of problem. But what to do if the whole MB is missed? Is it mandatory to do surgical treatment instead of non surgical ReTx? In case of short root and/or in case you can retroprep to end of cast post and seal all depth of root canal it can be as successful as non surgical Tx. BTW in this specific case non-surgical Tx is not allowed because of cast post restoration and crown.
One more proof that surgery works as well as non-surgical treatment and common misconception that the only non-surgical cleans and surgery only seals should be changed in our mind.