Can spirits escape, at least temporarily, the higher dimensions of hell? The Bible documents many cases of spirit possession, and these spirits can't be in hell and possessing people at the same time. Before possessing people, these spirits were roaming the Earth as disincarnate entities, (i.e. ghosts), were they not? Concerning these spirits, the Bible calls some of them devils, but has a variety of other names for them, such as evil spirits (Judges 9:23; 1 Samuel 16:14, 15, 16, 23, 18:10, 19:9; Acts 19:12, 13, 15, 16; Luke 7:21, 8:2), unclean spirits (Matthew 10:1; Mark 1:27, 3:11, 5:13, 6:7; Luke 4:36, 6:18; Acts 5:16, 8:7; Revelation 16:13), foul spirits (Mark 9:25; Revelation 18:2), and familiar spirits (Leviticus 19:31, 20:6; Deuteronomy 18:11; 1 Samuel 28:3, 9; 2 Kings 21:6, 23:24; and Isaiah 8:19, 19:3). Is there no room for ghosts here?

As for heaven, are there any scriptures stating that the inhabitants there are forbidden to help us down here on Earth? No. There are scriptures forbidding necromancy, (remember Deuteronomy 18:10-12 from above), but the Bible documents angels on assignment in numerous scriptures. Many of these angels may very well be the saints of ages passed, such as the deceased prophet who spoke with the Apostle John during his vision of Revelation (Revelation 22:9).

Revelation 22:9
9: Then saith he unto me, See thou do it not: for I am thy fellowservant, and of thy brethren the prophets, and of them which keep the sayings of this book: worship God.

So far, all of the explanations for ghosts I've mentioned using the Bible are actual disembodied spirits, but there may also be other explanations for ghosts that have nothing to do with sentient beings, such as thought forms, energy patterns science has yet to discover, fluctuations in the space time continuum, or people perceiving into other dimensions. In short, the world is very mysterious, and the realm of the supernatural is far too complex to label all that which is unknown as "demonic." Certainly the realm of the demonic has its place, but I personally think that Satan has been given too much credit for many things that don't have anything to do with him.