your google plus account only uses the regular, main google account.
the main google account is the one needed to log into the notepad++ community.

only the google plus platform closes down. (the facebook like platform that very few people use)
the regular google account, containing e.g. gmail, google calender, google contacts, android play store and google drive, as well as the single sign on to log into the notepad++ community and other pages, will continue to exist.

note: closing the main google accounts has not been announced, as disabling it would degrade all android phones to basically non smart phones, disabling any cloud based storing of contacts, calendars, over the air sync, google drive backups, the google play store, and many other features.

so if you still have an android phone, you are also safe at the moment, and you do not have to upgrade to an iphone right now, unless you wish to do so.
(the only cellular systems i recall, that had some core platform shutdowns lately, are firefox os, windows phone and rim blackberry services)