I don't remember seeing this paragraph before...
Picasa message" However, for those of you who don’t want to use Google Photos or who still want to be able to view specific content, such as tags, captions or comments, we will be creating a new place for you to access your Picasa Web Albums data. That way, you will still be able to view, download, or delete your Picasa Web Albums, you just won’t be able to create, organize or edit albums (you would now do this in Google Photos). "
If you want to copy and paste your captions from the old picasa web album photo's to whatever new site you use.... might be possible to do for a long time. (WHAT A PAIN)
I have noticed that google+ photos now have an edit feature to add text to the folder. Not to the individual photo's... maybe that's coming. Maybe they will ferry the captions across to google from picasa someday. I just can't take that chance.