Just to confirm, as various friends have been asking:

Note that photos and videos backed up in Google Photos will not be deleted.

So after Google+ shuts down April 2, everything you see at photos.google.com will be safe & sound. As for stuff not in your Photos library:

• If you’ve shared an image on G+, that shared copy will be deleted. You can see all of those images in the Album Archive page.
• You can download your content before the April shutdown.

Hope this helps. If anything is unclear, please let me know!