I would assume you get the support if you pay for it. Google, Azure and AWS seem to have all gone the same way. You select the service level and pay monthly fee. I don't know if this support covers Firebase.
Yes and no. If an AWS customer ran up a bill like this, Amazon would absolutely cover them. They've done it hundreds of times. There's a very different culture between Google and Amazon when it comes to customer service.
https://aws.amazon.com/premiumsupport/pricing/
https://azure.microsoft.com/en-us/support/plans/
https://cloud.google.com/support/