Is it complete shut down of perception and detachment of physical world?

This is what happens. When a person dies during coma or unconsciousness state, that person comes out of coma, becomes conscious.

This is not similar to Nirvana.

Nirvana is understanding the cessation of thoughts.

Coma and unconsciousness are continuation of thoughts. Coma and unconsciousness do not lead to the understanding of the cessation of thoughts.

The word "during" during coma or unconsciousness does not apply. It applies only to you who is consciouss. To the one who is in a coma or unconsciouss state, it does not apply. Thus, there is no "during" for the person in coma. There is only "now" and "now" for the person in coma. "Now" before coma and "now" after coma. "During" is only for you who is not in coma. What is between "now" and "now" for the one in the coma? Is there something? Or is there nothing? I guess you must find out.

As we know people who stay in coma or unconsciousness "experience" timeless,space-less, absolute emptiness and total detachment from physical world. Even though I used the word "experience" will not suitable to describe the situation in coma or unconsciousness state. It is a condition with no happiness or sorrow, no pain,no darkness or light,no noise or sound etc....and finally we can say "unconditional state of mind." and closer to description of "Nirvana"

In theravāda, this question's base-knowledge is ucchedadiṭṭhi, diṭṭhadhammanibbāna [nihilism&hold the doctrine of happiness in this life], rūpa-attato-sakkāyadiṭṭhi [form (the body) to be the self].

1. what happen when person die during the coma or unconsciousness state?

In abhidhamma, person still has mind's arising until person's citta-ja-rūpa, such as breathe, still going on. But because of karmma (kamma), temperature (utu), and nutrient (āhāra) are not good enough to support mind to done mind's job, such as making-nerve-impulse (citta-ja-rūpa), etc. So, the tool of the scientist can't catch mind's arising of this person.

That's the reason why some vegetative state can awake again, after long sleeping.

2. Is this similar to Nirvana? (as total detachment of world.)

Definitely no. Because buddhā said in Sutta. Saṃ. Sa. Dvādasamaṃ āḷavakasuttaṃ:

(The Blessed One:)

12. “With faith you cross the flood

and with diligence the ocean

With effort end unpleasantness

and with wisdom purify yourself.”

Thinking that with death and the break up of the body of a Realized One that some real thing utterly ends contradicts the doctrine of anatta and was specifically refuted in Pali Canon Sutta.

It is a condition with no happiness or sorrow, no pain,no darkness or light,no noise or sound etc....and finally we can say "unconditional state of mind." and closer to description of "Nirvana"

Actually that's far from Nirvana. If that was the case any sleeping newborn baby would've been in Nirvana without the need for any Dhamma cultivation. A person in a coma might seem to be at peace and without happiness or sorrow, but hidden in those deep layers of his consciousness are still the seeds of defilements, of greed, hatred, and ignorance. As long as these "fuels" are still there and have not been eradicated, the Samsara cycle still goes on for him. In constrast, a person who has attained Nibbana has perfect awareness, but due to the total elimination of all the "fuels", s/he's able to be 100% at peace while being 100% conscious.

No. If you are unconscious or in a coma then you are not laying there in a blissful state. Chances are your bodily functions are ticking over and there will be some brain activity. Just not enough to say or do anything. You can get a "lock in" syndrome where you can think but just not move your body. To the outsider you appear unconscious but you are fully awake inside.

There is a HUGE difference between actively "doing right thing" and "not doing something bad" because you are unconscious. If you were made unconscious while holding up a bank, then you will probably still have bad thoughts.

No, it is not nirvana. Nirvana is you coming to terms with the world, and your place in it. It is not imagining yourself floating on a sea of lotus petals. If you die in a coma, you don't get to say goodbye to anyone.