I'll answer this using the words of a former neighbor who, when asked why he kept three vehicles when he could only drive one at any given time, said "Unlike horses, they don't cost me anything to sit in the yard."
I see G+ much the same way. No matter what is said, no one knows for sure what's going to happen with G+. However, if you're looking closely, many of the earliest adopters and staunchest advocates have cooled to it, preferring to devote resources elsewhere, such as Facebook or Twitter or even newcomer Blab.
I'd say do the same: till the most fertile ground for your brand.
If you've invested in G+ and have a large audience who shares and engages around your content, continue to nurture those relationships. But to cover your bases, begin building relationships elsewhere, too, on platforms where your prospects are likely to congregate. Begin by following the influencers, sharing and engaging around their content. Share your content there as well, then enlist the help of your G+ followers - many of whom are also on the newfound platform - to amplify and engage around your content.
In this way, you're plowing new ground continuing to tend your existing flock.
This approach ensures that you're not beholden to the whims of Google and you needn't fret over what becomes of G+.
RS