Or HaChaim on Genesis 49:33/אור החיים על בראשית מ״ט:ל״ג

1 ויכל יעקב לצוות, Jacob finished commanding his sons, etc. This verse teaches that Jacob was an exception to the rule proclaimed by Solomon in Kohelet 8,8 that on the day someone dies he is no longer master over his spirit. Jacob was in full control of all his senses when he made all these arrangements. Only after having concluded all he wanted to say, ויאסוף דגליו, he gathered his feet into the bed, etc. Here is the source of the statement in Taanit 5 that "our father Jacob did not die." If death had taken possession of him, he would not have retained control long enough to be able to put his feet back into his bed. Midrash on Kohelet 8,8 explains that on the day of death a man cannot say to the angel of death: "wait for me until I have concluded my business and then I will come."