Hah! Wait till Mickey Rodent shutdown this game.....without warning!
No, they will warn before shutdown the game for iOS/Android. For the Windows they warned 30 days before that the game would be discontinued, but they should tell us something like this: "The game will be discontinued, but you can keep buying crystals from our store anytime you want. Keep enjoying our game and buying more crystals before the game closing. MTFBWY!"
Yes, that sucks! In the last maintenance i was waiting more 30min to finish my sentinel upgrade to upgrade it again for level 20 with more than 150k CB in safehouse and attacking while waiting. I went offline with no defenses and have a defeat by 100 % and lost almost 20k CB. If they warned, i could use a few crystals to finish the upgrade and start to upgrade again, and active my defenses. But Devs don't care. It costs too much work for them put a pop up to warn the game will be under maintenance or updating about 5, 10, 15 or 20 minutes before.
Except of course if you could buy an option "Warn me when game go for maintenance or update", like 10 crystals for 30min or 20 crystals for 1h before. I bet Devs will work on that as fast as they can...