The OS is alive, its in pretty rough shape still, but its alive. The future is in question though for current handsets. It seems likely that MS will reboot their mobile offering again with a 'W10 on ARM' release, its unlikely that it will be available for older hardware due to it requiring at least an SD820. Many Windows Phone users are going to be left behind again it seems.
The hardware is almost completely dead apart from two phones (HP Elite x3 and Alcatel Idol 4S). Lumia's are completely dead. There are currently no future handsets announced, although there is a rumour that HP might make an additional cheaper handset. There is also a startup company called whartonbrooks that are planning a phone release, I wouldn't pin any hopes on that though.
Apps have never been great on WP, but there was always hope with many new apps being added to the platform. Unfortunately the opposite is now true, with many big name apps leaving the platform, and many smaller Windows Centric developers now also abandoning the platform.
OS - Alive for now
Hardware - Almost completely dead
Apps - Dying, and quickly too
To clarify, I'm a Lumia 650/950 user, and Windows Phone fan. I see little value on sticking with the platform in 2017 though, its only remaining positive is the start screen / live tiles. Everything else is better on Android or iOS at this point, even speed, which used to WP's biggest selling point. I also own a lowly Moto G3 on Android Marshmallow, and it can complete 99% of tasks faster than my Lumia 950, which is just sad.