The fact the Protestants were as bad as the Catholics doesn't matter, because even with Adolphus, the Protestants don't conquer and force conversion of Catholic lands. If there is no Adolphus, then Catholics do take over Protestant lands. So how bad or not the Protestants are is not even important. The Catholics still use their power to use kill and forcibly convert Northern Germany. The resulting hardship would of been huge.
Next, most modern historians agree that the death rate was only 15-20 percent. The Thirty Year's War by Geoffrey Parker, and Simon Adams does a good job on covering the death rate of the war. Also the worst years of the war occurred after Adophus' death, during the French phase of the war. The Franco-Sweden alliance cause a huge amount of damage. If Adolphus lived, there is a good chance this era doesn't happen. Also I would argue, that the Peasants war, you end up something similar.
I agree with you on the last part, but this point is far to late for that to actually happen. There is far to much bad blood in the air, and the results for a victorious Imperial power would of been just to horrific in the North. Oddly, more then likely a victory by Adophus, the war would of been over soon after. The protestants didn't have the power to take the whole of the empire, and also the empire was not going to take the north. This would of forced them to make a peace to end the war. Also, if you want to get techincal, without Adophus, there is a great change Sweden is a lot weaker, and maybe even weak enough for the Danes to force Sweden back into its sphere of influence. Then the Danish portion of the war would of been so much worse.
The best way to save a large amount of lives is if the war had not begun in the first place. I think there are chances this war could of been put of, at least.