Apparently NPAPI-plugins are being discontinued because they are becoming obsolete and/or unsafe.
From what I read on this help page, if some plug-ins are to be replaced, they will be PPAPI instead, which is newer and safer. Most used things are included with Chrome, so support will not stop for those things (think PDF and their edition of Flash).
The discontinuation of NPAPI isn't a bad thing per say. The web evolves and things are going HTML5.
Flash and Silverlight are slowly becoming obsolete and their support declines.
NPAPI removal shouldn't be a reason to switch browsers, Mozilla also "encourages website developers to avoid using plugins wherever possible".