Resurrection of Christ, page-873

The spirit returning to God -> breath of life, your last breath.
Breath is one of the definitions of spirit.

"Isn't your spirit the true you?"

The you is what's stored in your brain and what is produced from it, is referred to as spirit, soul, your heart, mind etc, etc.
Your words are referred to as the spirit of you, for example.
Not to mention, we are not the follow the spirit of the world, which is simply referencing it's ways, as per the above here.

We are to live in the spirit and not in the flesh and I would suggest the spirit reference here is referring to God's Spirit, his way, hence the aim is to have his Spirit indwelling.
In Jesus's case, he had it without measure John 3:34

Hence, the Spirit returning to God imo, is very weak to go on, for what you're suggesting.
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Tell me Kam, lets say we all sleep as I have suggested it looks to be the case, what or how would that effect your faith and thinking?
If the immortal soul case was false, what implications would that have on it's followers?
If it was false, you would have to say that that teaching is coming from the opposition, proposing that you have life within yourself, where as the truth of the matter is, God sustains all life.