Offline first applications

Hi,
new to meteor, I have some questions about meteor and the “offline first” requirement.
I’ve understood that meteor use a minimongo on the client and it stores some data synched with the server. My point is, what happen if we close the web page or the app ? It seems data are lost because minimongo is more a proxy than a real storage location.
So, what are your best solutions to really store data in indexedDB in example ? I’ve found https://atmospherejs.com/mrt/offline-data?q=offline
Does that “fail” will be corrected in the next features ?

Check grounddb: https://atmospherejs.com/ground/db