Care should be taken to differentiate between two entirely separate legal categories of discovered artefact, that which is classed as "Treasure" according to the 1996 Treasure Act, and that which is merely a so-called "Portable Antiquity". Anybody, whether an artefact hunter who has gone out equipped to find such items, or somebody who finds something accidentally, walking the dog or gardening, is obliged by law to report the discovery of a potential Treasure item to the relevant authority within 14 days. It's the same with human remains in the woods, you are obliged to report it to the Coroner. A finder of a non-Treasure item is not obliged to report the items (so, like the equivalent of finding a dead dog in the woods if no crime seems to have been committed).
The 1996 Treasure act is clear, the find of a Treasure item should (in England and Wales) be reported to the Coroner, not the PAS. It is in the hands of the Coroner that the initiation of the whole "Treasure process" is vested by law. Most metal detectorists will say that they and their pals are all law-abiding, and on any hobbyist is incumbent the obligation of knowing the laws that govern that activity. It therefore seems that removing the PAS from the scene in Wales would not reduce the number of Treasure finds being reported by law-abiding "metal detectorists".
This is an important distinction, because over in England, the steady increase in the number of reported hoards and other group finds classed as Treasure by English law being processed by the system is treated as an index of the "success" of the Portable Antiquities Scheme (which is actually a totally separate organization set up to deal with something else). An example is Bland 2010, fig 6.3. At the same time the apologists of artefact hunting (in which we may class the PAS itself) stresses that the "vast majority" of English artefact hunters are law abiding searchers of history, "not in it for the money". Nobody explains however how, in that case, the rising number of Treasure finds reported each year is not an index of the rate of erosion of the archaeological record by the selective removal of assemblages of associated objects from the archaeological deposits and their original context which extremely commonly can never e reconstructed even if the site is subsequently the focus of a small-scale archaeological excavation.
In actual fact the process for fulfilling the legal obligation of reporting Treasure in Wales does not need an expensive Portable Antiquities Scheme - it s enough for finders to be made aware of the addresses of the local Coroner's office.