In the case of open source project,
* if the maintainer is no longer able to take the project further, the code is still there an can be used as is, maybe with a few bugfixes. (ala, thunderbird). The code does not disappear overnight. r.
* All the associated data is still yours and available. So no information is lost.
* If it is very critical, you can develop it yourself further
I am not an user of Inbox, but I can understand the outrage. When a service is offered for free by such a mammoth of a company, it gives a false sense of security and permanence. It crushes most competition and development of open source alternatives. Then one fine day, the rug is pulled from under your feet and there is no recourse.
The most ironic aspect is you no longer have access to your pinned emails, bundles and such. Yet, somewhere in google's distributed data storage, it will continue to reside for a long long time. The information asymmetry is outrageous.