The stopping of /e/ is unlikely.
This is mainly due that the foundation is a non-profit organization and does not depend on financial goals like Google or Apple.
However, as with any free project, a decrease in contributions may lead to a slowdown in development, or even to its abandonment in extreme cases.
This is also the case for other free projects such as Ubuntu Touch from UBports, Postmarket OS, and even LineageOS or Libreoffice.
But even an abandonment of the development team is not necessarily synonymous with the death of the project. The most telling example is the discontinuation of Ubuntu Touch by Canonical; the project has been taken over by the UBports foundation and continues its development.
If, despite everything, /e/ were to stop and no one took over the project, then yes, the online services would be stopped.
But I repeat, this scenario is very unlikely to happen.
I rather think that because of the current evolution of technologies aiming to control more and more populations (without wanting to go off topic), will give even more credit to projects like /e/.
All this reflects of course only my personal opinion…