Well, it looks like subcutaneous injections off silicones do see small molecules of it wrapped in vacuoles in the blood (though the injections are of fluids, so can't be certain of the breakdown of more solid forms [https://pmc.ncbi.nlm.nih.gov/articles/PMC6358378/]). Silicones do burn, producing silica powder, which means it is subject to oxidation-reduction reactions in some manner. Some silicones break down readily in organic processes. The wikipedia article notes clay as being particularly catalytic. The medical grade silicones don't have even that little bit available for long term study (especially of the thousands of years variety you'd need for this picture), but I'd take a wager even they would eventually decay. Buuuut, the decay would likely be slower than skin/organs.