Q: Do dreams necessarily give us information of future happenings of events concerning our lives? And when in a dream is our spirit still in us or has it temporarily abandoned our body?
A: Dreams have always been a subject of great interest to us humans...some of them can be so vivid that we can't help but feel that they have meaning in our waking life; however, The Urantia Book is very clear on the subject of dreams:
110:5.4 While their mortal hosts are asleep, the Adjusters try to register their creations in the higher levels of the material mind, and some of your grotesque dreams indicate their failure to make efficient contact. The absurdities of dream life not only testify to pressure of unexpressed emotions but also bear witness to the horrible distortion of the representations of the spiritual concepts presented by the Adjusters. Your own passions, urges, and other innate tendencies translate themselves into the picture and substitute their unexpressed desires for the divine messages which the indwellers are endeavoring to put into the psychic records during unconscious sleep.
...your ordinary dream experiences are purely physiologic and psychologic phenomena.
And I think I can add here that our dreams are not prophetic; they are not meant to provide clues to future happenings in our lives. In man's long-ago past, dreams took a prominent place in his mind simply because they could not be easily explained or understood, but with the dawn of modern science, dreams are now seen as merely a necessary part of our inner mental makeup.
Dream interpretation is not a reliable method of understanding our waking lives, nor will we benefit from spending a lot of time trying to interpret dreams. They can be interesting sometimes, but they are not a solid base from which to understand your waking life.
Our divine Adjuster does not ever leave the mind of its indwelling during the dream state, as far as I know. Instead, as in the quote above, the Adjuster attempts to give us inspiration and spiritual content in our superconsciousness during our dream seasons, but they are seldom successful.
Physically and psychologically speaking, dreams are a method of the brain/mind mechanism to reconcile and straighten out events and conflicts of the waking life. Dreams are a necessary part of good mental health, but—with very rare exceptions—dreams are simply psychological phenomenon, and not to be paid overmuch attention. Better, we will benefit greatly by cultivating a solid relationship with heavenly Father in our waking life, which is where make decisions and seek for God's will.
Thanks for your inquiry!