Thanks for asking our question here at TruthBook.com. You asked: "Will the earth end in fire and lava or in ice?"
I guess I'd have to say: one or the other, destruction by fire (supernova), or ice (dwindling solar output), appear to be the only choices presently offered by science regarding the ultimate fate of a planet or sun. They grow old, they eventually die.
The Urantia Book describes material reality in super-scientific terms, in terms that go beyond the current limitations science imposes upon itself, by making it clear that the physical universe is an expression of spiritual reality, that matter is under the overcontrol of spiritual force, that God created the physical universe and controls its destiny.
In Urantia book concepts, worlds that harbor intelligent, free-will life begin the long evolutionary journey from a primitive struggle for existence up to a golden age described as light and life, a kind of heaven on earth. When light and life are attained on a planet it and its sun are stabilized in the energy circuits. The sun does not self-destruct, the planet and the life it harbors goes on into infinity.
As a world inhabited by free-will creatures, earth is destined to become a planet achieving the era of light and life sometime in the distant future and at that time the spiritual power directors will stabilize the energy circuits of the sun and the earth. Between now and then however there is no guarantee that civilizations won't rise and fall, flourish and disappear, just as they have in the past. We do believe though, that the physical destruction of the planet will not be allowed to happen, despite what civilizations may do to one another, for, as The Urantia Book says:
Urantia is the sentimental shrine of all Nebadon, the chief of ten million inhabited worlds, the mortal home of Christ Michael, sovereign of all Nebadon, a Melchizedek minister to the realms, a system savior, an Adamic redeemer, a seraphic fellow, an associate of ascending spirits, a morontia progressor, a Son of Man in the likeness of mortal flesh, and the Planetary Prince of Urantia. And your record tells the truth when it says that this same Jesus has promised some time to return to the world of his terminal bestowal, the World of the Cross. (119:8.8)
I am sure that this will happen. It seems unlikely to me that the planet will be allowed to destruct simply because Michael chose this planet, and I am sure that he has a sentimental attachment to it, just like we do!