You'll get that prompts for the remainder of the event. If you click the yellow arrow and then click the x to get out of the screen you can ignore it...
Hst, they're absolutely not the only developers doing this, and in my experience they are better about trying to keep the game playable for a longer...
I don't interpret Playrix' silence as good often either, but wow, you state some pretty astonishing things as facts there. Where did you get all this...