Rashi: If I would die, I would not thank You for the miracle of the fall of Sancheriv. I did not expect [to see] fulfillment of what You promised me about him.

Radak: It is good that people scream in front of You when they repent from their sins, for they thank Your in their lifetimes; they do not thank Your in their death. He refers to the body, which dies, but not the Neshamah, which lives after the body dies.

Radak: "Lo" applies also to this. There are many verses like this. The matter (the dead will not praise You) is repeated three times, to strengthen it.

Radak: The bodies, which die, do not look forward to Your Emes (Malbim - fulfillment of Your promises) to tell it like the living do. He does not discuss Techiyas ha'Mesim, rather, when the bodies are in the grave. And not all bodies rise from the grave.