Has Gmail shut down yet. Google photos is not going to shut down. Why? Because of data photos are data billions of megabytes of data that is being uploaded to Google every week. I don't think Google would want to miss out on it.
It could easily happen that Google comes up with a new product they think should replace Google Photos so that they shut down photos to force-migrate users. Wouldn't be the first time.
I hope they do commit to Google Photos growth momentum over profit seeking, but hard to be optimistic these days based on their recent record (and no I'm not talking about Google Reader).