Assalaamu `alaika warahmatullaah, brother.
I cannot know with 100 percent surety until I die.
With all due respect, you seem to have a serious problem with `ilmul ghayb (knowledge of the unseen, which none but Allaah knows).
But the works of people like Zakir Naik, are a proof that the Quran came from a divine source, but not necessarily from the Creator.
So you're basically saying there's a "divine source" out there but it isn't Allaah? How many Divine Sources do you believe there to be? Who created the Universe, the galaxies, the Earth and the Sky and all that's within them? Is there another Creator besides Allaah? Another Originator besides Allaah? Another One who takes life and gives it, besides Allaah?
Brother, before I go to a library to get that book by Dr. Grof (or buy it from Amazon for $5), I'd like you to study Tawheed in it's entirety. Study `Aqeedah. You shouldn't go around reading books by non-Muslims about "the dead", or whatever else that deals with life outside of this dunya, without first having a firm belief in Allaah `azza wa jall. I'm not saying this because I'm keeping you from really finding out the "truth" that's out there or because I'm afraid you'll find out the "reality" of what/how Islaam really is, but I'm saying this for your own good. If you're firm in your `Aqeedah, you should definitely be able to distinguish between truth and falsehood and there'll be no room for doubts such as this.
This Dr., Stanislav Grof, has no knowledge of Allaah `azza wa jall. He was once a disciple of
Freud. (some of his *theories* are just appalling) These guys, their work is based on "theories" and a few experiments here and there. You can't come to a conclusion about Islam by reading their work. That's not what a man of sound mind would do.
I also think that you're having doubts about the concept of "mawt"(Death) and not
all of Islaam, right? Could you maybe point out a few things you don't agree with isntead of making us read a book (that if I have to be honest, we could all do without) and we'll try to shed light on them to the best of our knowledge inshaa'Allaah... And, by "expert answers" I think you meant scholars? Sorry, we're all just regular folks here not scholars.