You can easily check to see if you have been using photo stream or see if you even have the option to use it.
First, launch the Photos app and look for an album titled Photo Stream. If you have no such album, you have no worries.
You can also check in Settings>Photos. If you have a photo stream option it will be visible in there. If you don’t see the option, you don’t have it so once again, no worries.
If you have the option but you never enabled it, … no worries. You aren’t using it.
Even if you are using Photo stream, all of the photos in there are on one of your devices and when photo stream is closed down, you will keep the photos on that device.
This is a worthwhile read, so take a look.
Information about the My Photo Stream shutdown - Apple Support