What should be done for an extremely sloping flat forehead and brows that are angled into the crevasse of nose?

It is impossible to see full extent of your "deformity" on these photos, unfortunately. However, it looks that combination of forehead lift (hairline or endoscopic) with forehead contouring with cement, HA granules, fat grafts, permanent filler, would be  good procedure for you. Only on the basis of in person evaluation an experienced plastic surgeon with good reputation in this type of surgery can make right selection of procedures. Good luck.

Medial brow depression and angry look and brow bone excess? All of these issues can be corrected with an Irregular Trichophytic Forehead Lift with or without hairline lowering. I have done more than 500-1000 of these without problems and a near invisible scar. See several very experienced surgeons who can show you natural results and no visible scar.

There are two important issues to consider: (1) your present aesthetic disharmony and (2) what will happen as you age. Although your photo is not a "true" lateral (side view), you appear to have a retrusive forehead with a horizontal contour depression. Your eyebrows are low, especially the medial (closer to the nose aspect), your lower lids appear a bit prominent because your medial (toward the nose) cheekbone is a bit weak or depressed, esp relative to the lateral (or toward the ear) cheekbone. We age by bone and fat loss, and therefore your forehead (upper facial third) to lower facial two-thirds disharmony with becoming worse if not treated. I believe bone loss occurs because of deteriorating circulation as we age, especially after age 45. Fat grafting, the body's most potent stem cell will not only reliably and consistently treat your issue long term, but it will help restore circulation to the bone and prevent exacerbation of this aesthetic disharmony as you get older. 

To clarify some of your misconceptions about forehead augmentations, implants are made of a solid material and do not fail or rupture. I have implanted the forehead with bone cements and custom implants for thirty years and have never seen an infection. But to answer your specific questions, fat injections are done with very small cannulas and leave no scars to do so. Any form of injectable filer is going to be temporary. No form of forehead augmentation canes the shape of the the brows. That has to be done with browlifting techniques.

The pictures suggest you have prominent bones under low eyebrows. If you have a high hairline I recommend you consider the Irregular Trichophytic Hairline Incision Technique that I developed and described many years ago. With this approach the brows can be lifted, the orbital bone reduced and contoured, and the hairline lowered if necessary, all at the same time.