The Gemara in Taanis (דף ה:) tells us that Rav Yitzchak once surprised Rav Nachman by telling him that יעקב אבינו לא מת, our father Yaakov never died. In trying to understand this statement, Tosafos (שם בד"ה יעקב) explains that the Posuk which describes the demise of Yaakov does not use the word "וימת," "and he died," but only "ויגוע," "and he expired" (בראשית מ"ט:ל"ג). Indeed, the earlier Pesukim which tell us of the deaths of Avraham and Yitzchak use both words, ויגוע and וימת (עיין שם כ"ה:ח',ל"ה:כ"ט), while in our Parsha, the Torah uses only the one word about the death of Yaakov. We must ask ourselves, however, what exactly this statement, declaring Yaakov never to have died, means. The words of Tosafos (שם) serve only to deepen the curiosity and not to solve it.
Perhaps this idea can be explained by understanding the attributes, the מידות, for which each of the Avos was known. The מידה of Avraham Avinu was חסד, kindness. He was the one who invited guests and who took an interest in others with the hope of placing them onto the path of Hashem. We are taught that the trait of Yitzchak was גבורה, might, which manifested itself in his worship of Hashem. The religious personality of Yitzchak is symbolized by the Akeidah, the ultimate act of worshipping Hashem. Finally, Yaakov possessed the מידה of אמת, truth. The formation of the Jewish people took place as a result of the combination of these traits of our forefathers.
In his ספר מכתב מאליהו, Rav Eliyahu Dessler explains why it was so important for the מידות of Avraham and Yitzchak to pass through Yaakov before they were bequeathed to all of the Jewish people. Both the trait of חסד and that of גבורה are wonderful and fine traits for a person to have, but they include the risk of being misunderstood and misused. There can be nothing greater than for kindness to be inculcated into a person, but sometimes kindness can be misplaced. For example, it is misguided to show undue kindness to an evil person who must be punished. Similarly, גבורה, when used in inappropriate places or in extreme measure can be detrimental. One must thus apply these מידות correctly in order to use them for the proper purposes. Therefore, the trait of Yaakov was אמת. With the truth as his guide, Yaakov could teach to his children how to make good use of the חסד and גבורה inherited from Avraham and Yitzchak.
This may explain the Torah's use of the word וימת"" regarding the deaths of Avraham and Yitzchak, but not regarding the death of Yaakov. When Avraham and Yitzchak died, there was an end to their use of their particular מידה because, while they certainly knew how to use their personality traits properly, they could not be certain that others would as well. Therefore, the Torah uses a word of ultimate finality: וימת. Yaakov, though, who represented אמת, was the filter through which חסד and גבורה would reach all of the Jewish people. He refined these concepts so that all could benefit from them and utilize them properly. Therefore, the word וימת is not used. The traits do not end with Yaakov. They pass on to us, thereby insuring that indeed יעקב אבינו לא מת.