Yep, what Sumeragi said basically. Kim Jong Il had already accrued a pretty significant amount of power by 1994, having essentially been groomed for leadership over decades and by that point ruling alongside his father. If Fujimoto's testimony was right, and the pressure was getting too much and he decides to kill himself, we're likely to see his uncle take his place. His sister Kim Kyong Hui and her husband Chang Song Taek were supportive of Kim Jong Nam taking over, so he might be groomed for leadership.
I would think that in the absence of the Kim Jong Il's manipulative leadership and ability to balance generations and agencies within the regime, shit could go down relatively quickly. KJI's half-brother Kim Pyong Il might have returned and started trouble (KIS prior to his death is alleged to told him he was sorry he wasn't more supportive to Pyong-il).
The fact that there was, prior to 1994, two man leadership had led to the development of a faction of old-generation hardliners centred around KIS, and a younger generation faction centred around KJI. If both men died, they would lose their immediate patrons. Following that, they could align with Kim Yong Ju, Kim Pyong Il or a powerful figure outside of the Kim family.
This would, more likely than not, lead to divisions and conflicts amongst the elite, which combined with the economic malaise, the fall of the Soviet Union and other such factors would most likely lead to a Romania-like situation of elite-faction-sponsered military or civil rebellion that knocks down the government.
This could lead to total collapse and incorporation into the South, though there would require more assertiveness from Seoul in this period I think. On the other hand, it might lead to the formation of a collective leadership structure like China and Vietnam able to break with Juche and pursue economic reform. The odds of unification in some form would be significantly improved in most scenarios, I think. Unless a member of the Kim family is able to hold onto control.