Facebook has stated that the sharer.php is deprecated. https://developers.facebook.com/bugs/252983554810810/

It appears to have an unclear lifespan. While it has been fully replaced by the Feed Dialog, it's still working now and is used all over the internet. I can see the case where it won't see any further development or features, but it's a tough call whether or not to incorporate the deprecated method or accept possible risks of the current methods - Like button or Feed Dialog.