While I was initially optimistic about the idea behind PlanetSide Arena, the longer the development went on the more obvious it became that it simply wasn't as interesting as PlanetSide 2. And for a spin-off game that requires large amounts of players in order to launch even a single match, that wasn't exactly a good starting point.
As such, when PlanetSide Arena finally got released into beta, it did so to a rather tiny playerbase. Things only got worse from there as the already small community quickly started bleeding players until pretty much nobody remained. Since developing a game that nobody plays is in no way sustainable, it unfortunately won't come as much of a surprise to hear that PlanetSide Arena will be closing down its doors on January 10, 2020.
"While our team set out with an ambitious vision for a game that combined the massive-scale combat and camaraderie of PlanetSide through a diverse collection of new game modes, it has become clear after several months in Early Access that our population levels make it impossible to sustain the gameplay experience we envisioned," reads the official update. "As painful as it is to close this chapter so quickly, we remain deeply committed to this franchise, and look forward to continuing this journey through the PlanetSide Universe with all of you."
All DLC purchases have been removed from Steam, though if you have any virtual currency remaining on your account, you'll be able to spend it until January 10th. When it comes to refunds, worry not as the developers have already announced that all players who made in-game purchases will receive a full refund to their Steam Wallet shortly after servers shut down on January 10th.
You can learn a little bit more about the shutdown process, as well as PlanetSide Arena itself, over at Steam.