Leah died some time before Jacob (according to Genesis 49:31) but we are not told exactly when. Please cite a source as to exactly when Leah died.
Seder Olam Rabba says that Leah passed away in year 2216 after creation, 9 years after Rochel, in the same year that brothers sold Yosef to Mitzrayim. Rochel died when she was 36, so Leah died when she was 45.
More precisely, this is in the 2nd chapter of Seder Olam Raba. The Vilna Gaon derives there that Leah had to pass away before Yosef was sold.
The Sefer Hadoros page 54 writes that Leah died in 2214 at 51 years of age. Or she died 2216. Others say she was 44. Some say she was born 2163, 2164 and twins, others 2170.
Interestingly, There is a Midrash Rabbah 92:5 that says, ““They sat before him, the firstborn according to his seniority, and the younger according to his youth, and the men wondered to one another” (Genesis 43:33). “Joseph hurried…They sat before him…” – he took the goblet and created the false impression that he was smelling the goblet. He said: ‘Judah, who is king, sits at the head. Reuben who is the firstborn, will sit alongside him,’ and likewise regarding them all. He said: ‘I have no mother and Benjamin has no mother, when his mother bore him, she died. Therefore, let him come and place his head alongside mine.’ That is why, “the men wondered…”
The question is, the mother of the other brothers at this time had also already passed away, so why did he exclude the other brothers from this loss of a mother? So, at this time, Leah was certainly no longer alive.
Perhaps one could say that at the time of Rachel’s passing Yosef was about 7 years old. Not having a mother at that crucial age in development leaves a traumatic emptiness. When one loses their mother at a later age when they are grown and have already been emancipated and independent, it does not leave as much of a hole.