Okay, so what you need to understand is that most of these skulls have not been excavated properly, meaning, they have been dug up from graves where grave robbers have destroyed all relevant historical evidence decades, sometimes centuries ago. Most of them have travelled through a serious number of traders` hands and through private collections before they have ever arrived in a museum, and even then, for some of them, it`s rather hard to place them in any form of hisotrical context. This has opened them up for a lot of non-scientific speculation and far fetched theories.

The skull you`ve posted is currently located in the skull collection of a Osteology Museum in the US, and it has arrived there with little to no contextual evidence of the burial it has belonged to. One of the few qualities that allow to roughly date and place it is the shape of the skull. A large number of skulls shaped like this one, for example, have been found in south-eastern Peru, in an area known as Colca valley, in graves roughly dated in between 1100 to 1450. Elongation, most likely, has been a sign of higher class birth for these people, and was performed during the early years of infancy while the skull was still soft enough to be shaped. This doesn`t neccesarily mean that this particular skull comes from there, too, but yeah, it means it can, indeed, be from Peru and dated to that timeperiod or earlier. Meaning the skull can be at least 600 years old or older than that.

There has been evidence of spectacular medical skill in some peruvian skulls from roughly this time period. There is a whole number of skulls with holes drilled into different areas of the skull, as if someone wanted to ease pressure. Some skulls show traces of inch wide pieces of skull cut out or drilled out, either to ease pressure on the brain, or to remove fractured bone, and some skulls even miss enitre sections of skull where it is assumed large scale skull fractures have been corrected. Most of these holes, however, do not show any sign of healing of the bone, and if they do, not many have actually healed all the way over. Those that show traces of regrowth of bone usually only show smoothed over edges or first traces of bone structure reaching out to cover up the hole; meaning there`s little to no evidence that these people survived the surgery in the long run. They may have for some time, since there`s evidence of several holes drilled with different healing stages on the same skull, but it is generally assumed that infection must have killed them if not within days then within months of the surgery. Then again, we don`t know why these holes would be inflicted on the person to begin with; it could be linked to head injury, to headaches or bleedings, and in case of those elongated skulls, also because of building pressure caused by the deformaty. There are even some theories proposing it could have been out of religious reasons. We simply don`t know, and at least for some examples, that makes it impossible to tell if it has been the surgery who killed them in the end.

Closed fractures, on the other hand, were something entirely different. The skull on your image has a rather large fracture that has been well on its way to healing, however, it seemed to have been a comparably smooth fracture, and while there must have been a large amount of pressure onto the brain, chances are good that there was little to no real open wound to the outside. Wounds within a certain limit might still have been treatable with the antibacterial means of ancient medicine, such as honey etc., thus healing of such a wound was not impossible, but as soon as the brain has been opened up, it is not very likely that the person survived in the long run.

This leads us to the metal involved. There are researchers who follow the theory that the pieces of bone drilled or cut out were not put back into place but replaced by pieces of silver or gold foil. Sadly, since most skulls showing these surgery marks come from abovementioned robbed graves, there is no evidence of any such silver or gold plates found anywhere. It is, however, logical that especially large scale wounds must have been closed up somehow, at least for the short period of time we have evidence for healing, but there is no real evidence for how. Then again, there is no evidence against it either, since there are just about two or three mummy burials with evidence for skull surgery where the bone pieces can be found put back into place, although these pieces have been, most likely, glued back into piece during the burial preperation.

If this piece of metal has been put into place during burial preperation, too, or if it has been there during what time there has been during the healing process of the fracture can probably only be answered when the skull is looked at more closely. What I can say for certain, however, is that the metal has not been put in place while it was in liquid form.

Silver, if we assume it is silver, does melt at roughly 961,1 C°. This is way too high a temperature for bone to survive without clear evidence of burnmarks - and burnmarks do destroy bone to such an extend that it can not completely be washed away. At the very least the bone would have cracked due to differences in temperature and the brain behind it would have cooked due to the close proximity. There is no evidence for temperature cracks, nor burn marks, nor does the metal look like it has been poured.

So, to come back to your questions.

Certain forms of skull surgery have been rather common in ancient Peru, but survival chances, judging by the bone evidence, must have been rather slim. And it is safe to say that the metal can not have been liquid as it was attached to this skull, or that would have absolutely slimmed survival chances down even more. It could be silver, judging by it`s use in historical context, but it may be a later addition - so it can be anything, really.

It may have been not exactly a hail marry operation, since there are a lot of mummies and bone fragments showing healed fractures and a relatively well developed medical skillset, but infection was not something they could control or survive very well. Attempts at skull surgery, such as found in Peru, have been found all over the world, with roughly the same evidence for healing or lack therof, thus it can not really be compared. And frankly, not many people actually do research on the topic outside of South America either so anything beyond this point would be assumptions on my part.

I hope this covers at least most of your questions.