And if your mercury Dental amalgam is still in perfect condition, should you replace it?
At the end of the day there's massive amounts of data since these fillings have been in use for over 100 years, and it's quite clear who has them and who doesn't. If they do have actual negative effects, they are small.
Definitely better than having cavities, but modern composite fillings are probably better still (though, being plastic, there's the endocrine disruptor question on those - and a much wider range of composite filling materials out there makes it harder to study).
The safer choice is to replace all the amalgam fillings with composite fillings, unless you cannot afford that (but composite fillings are much cheaper than ceramic facets or crowns, which may be better choices when possible).
Anecdotally, I have replaced all my amalgam fillings more than 15 years ago and I have felt much better after that, because with the amalgam I had always felt an unpleasant metallic taste, while ceramic and composite resins do not have any taste.
Plastic ones probably will not last that long.
If the leakages from mercury or plastic are more unhealthy nobody knows. I will not replace mine until absolutely necessary.