This 'news' from the Devs on Steam might shed some helpful light on the delisting:
"Hey everyone,
For the past year or so we have been approaching WARSAW with ideas on how we can deliver on expanding the game in significant ways. We always felt that the deep and engaging gameplay, numerous colourful heroes to choose from and adherence to realities that Warsaw inhabitants faced during the tragic months of 1944 were strong basis, but wanted to be able to build upon them.
Feedback we received from players, media and creators helped us understand how the experience shaped their knowledge of Warsaw Rising, but also made it very clear for us that the story of those days is not commonly recognised both in Poland and abroad.
With that in mind we went back to work on further enriching the game with historical information, tied closely to the game itself, and allowing everyone who plays WARSAW - to have a better understanding of what happened between August 1st, 1944 and October 3rd, 1944 in Warsaw, Poland.
We hope to be able to share the details of what this really means with you very soon, but in the meantime we would like to ask everyone to REFRAIN from buying WARSAW going forward. We feel that the changes to both the game's contents and the pricing will be to everyone's favour, but in order for you to best take advantage of that - we would like everyone to not buy the game until the next time we post the message here.
It will happen much sooner that you think.
Thank you for your patience and stay tuned,
WARSAW team"
From August, 9th.