Earlier this year it was announced that King Tut's iconic death mask had been damaged by some incompetent curators - the beard had been knocked off! - and then hastily repaired using epoxy that ended up getting everywhere. My take at the time was that the epoxy most likely contained BPA (bisphenol A) and thus the mask was being exposed to BPA for all eternity. But that concern is now being addressed, as a German expert has been assigned to repair the mask [*]. Since the depth of penetration of the epoxy is unknown, the time for the repair is vague, with 2 months being the outer limit at present.
Apparently the construction of the mask is unknown (other what is on the surface) and so the repair team will take advantage of this opportunity to study it further. The details of the construction will then drive what approach will be taken to reattach the beard in a more suitable manner than the "Dumb and Dumber" approach taken last time.
I can't imagine what would be done to reattached the beard. A mechanical approach would stand up the longest and duration has to be a great concern. After all, this object will be retained for millenia into the future and adhesives - organic, silicone or any other chemistry - will not have that durability. If they are used, it would likely be with the view that any adhesive would have to be removable at some future date so that it could be refreshened. (No more scraping off epoxies with a wooden stick.) But a mechanical approach would also be the most invasive and damaging, even if the outer aesthetics are immaculate.
It possible that some good may come from the epoxy disaster. If epoxy did in fact penetrate the mask to some degree and then hardened, that material could then serve as a barrier to penetration from adhesives applied now and in the future. And that could put the adhesives option back on the list. We'll just have to wait and see what is approach is decided upon and what the justification is.
[*] How do you get a job like that? Is it a free-lance position and what are the hourly rates?