If you haven't studied archaeology or worked in the field, it is easy to overlook the importance of that last sentence. I can only speak for Germany and some neighbouring countries, but this could change everything.
Our current approach to preservation is generally to dig when the site is threatened but only to dig as deep as the threat to the site will go[0]. So if someone builds a house with a cellar that is x metres deep, we will only dig x metres, and clean and document all finds up to x metres. Even if it looks promising to dig deeper, it is quite usual to let everything that is deeper than x metres remain in the ground, and just document its existence. This does not only conserve limited resources, but it also means that there are archaeological sites for the next generation of archaeologists has something to excavate with newer technologies. These can then reveal information that we would destroy with our current methodology.
However, all of this is contingent on the assumption, that the ground which has been preserving the archaeological finds for the last couple of millennia will continue to do so for another century or two. If this is threatened by micropastics, our current approach is dooming a lot of sites. Though I believe a more proactive approach is probably not even feasible unless public funding increases by an order of magnitude, which is of course highly unlikely.
[0]: there are of course many exceptions to this, like purely scientific excavations. However, the majority of excavations in Germany are done because someone is building something on an archaeological site, and has to employ archaeologists so that the knowledge and artifacts are not lost to the merciless teeth of excavators and the like.