Sforno on Genesis 44:32/ספורנו על בראשית מ״ד:ל״ב

1כי עבדך ערב, the reason why he would die as soon as the lad did not return without even asking what happened to him is because I have guaranteed the safe return of the lad. As soon as he would notice that that I did not bring him back, he would automatically assume that something fatal had happened to him, and that I had been unable to make good on my vow on account of that.