[panzerfan]

And that's the thing. Rationally speaking, the impact of losing such a change agent is incalculable, and even if the prospect of it ever coming to that point (through natural causes and whatnot) is not certain, there exists this possibility for Haruhi is still mortal.

For when Haruhi stops, the data entity loses an evolutionary potential, the espers would lose the very thing that forced them into being and even if the future does exists, is it the Asahina view or the Fujiwara view that's more accepted? The impact on humanity would weight in from looking at the time travelers from Sasaki's vantage point.

I don't think Sasaki can make the call on whether if she can die or stops, but she definitely can see the problem coming if Haruhi stops or dies.