First, your entire premise is that Nasus is unbalanced. This is wrong. He REQUIRES stack farm to be useful in game; without it, his only thing is using Wither (hopefully on the adc) and then ulting and hoping he can punch you to death, slowly. If he does not have stacks he has NO threat, at all.
Second, Nasus is entirely balanced on not having stacks lost when he dies, since one of the main ways to put him behind is to kill him in lane. If this change WAS made, there would have to be massive buffs given to him, probably in the form of getting extremely high stacks per Q, lower cooldowns, and more reliability and power in his WER. That would put him firmly in feast or famine, which is not really a good place for a tanky mid game champion to be.
Third, if you really have problems just kite him. He can have 600 stacks, but that doesn't mean much when he can't even get in range to autoattack.