in my opinion, if he touch the scale the femboy won't die to because faileng said his soul failed to enter the scale
this is just my opinion
this is just my opinion
BL fan 
Comment by Shin on Summoning a BL Fan to Another World - Chapter 30
1 Reply
Leng said his soul was starting to be rejected because Kotone was there, which means if Kotone touches the scale, Asagi's soul will be fully rejected, and his body would return to his natural human age (which is over hundreds of years, which is why he would die)