Oh, hey folks.
Demon's dev here; thank you for all the interest in Demon! I've read through the posts up to this point and wanted to mention a few things:
1. You can disable Demon's (but not Unity's) data sending in the options menu, accessed with the - key. Granted, since I can't block Unity's, this does still mean blocking the app the only way to block 100% of it, but turning Demon's off will at least get rid of the server connection pop-up from when Demon tries and fails to connect.
2. The Tower itself currently has 23 floors, with several small side dungeons and one larger side dungeon. The bosses are largely static: I say "largely" because of enemy Summoners: enemy Summoners use an AI to choose the demons in their party and what abilities they've taught them, so while you the Summoners themselves are the same name, appearance, stats, and abilities, the demons they use change from game to game.
3. "Relic Preservation" (the mechanic that causes potentially lethal damage to first be doubled and taken out of your MaxHP, with death only occuring when both HP and MaxHP aren't enough) is relatively new; I don't doubt I may need a bit more UI/visibility on it.
But, until then, I'll go ahead and say outright it's possible to recover lost MaxHP via gaining XP, using MaxHP draining abilities of your own, or if you're desperate, using Pure Stones/Pure Gems.
I'll check in and answer any other questions / read any other feedback posted here from time to time.
Thanks again for checking out Demon, and good luck in the Tower!