I am sure this is the number 1 concern for them. If they don't solve this then they have just screwed themselves over.
Bigger concern: How exportable is this database (my guess is very, since its a resful api to access it all) because at some point if they fail, you going to need to move to your own cluster.
Whether the API is REST is irrelevant. In most big data use-cases on real systems, you have special dump/export tools to get your data out. In this case, the question is whether such a tool/API exists, how fast and practical it is. It can be simple though, eg. do they have a button on the webconsole that exports your dataset to a CSV file that you can then download per FTP.
Bigger concern: How exportable is this database (my guess is very, since its a resful api to access it all) because at some point if they fail, you going to need to move to your own cluster.