For variables in memory perhaps but I don't think that is true of file system variables is it?
Forgot to mention on this post that I moved to chat to the link below, as we are no longer talking about node red not starting
Just to answer that last question here, yes it is true of context with a file system backing. The data is still accessed from RAM just like the normal context, but it is flushed to disc occasionally, and picked up from disc on startup. However, if one does not call flow.set() then it does not know that the data in the cache has changed so it will not be flushed, so a node-red restart, for example, would lose the recent changes.
As @alex88 has started a new topic about context and is copying over your replies to keep it in sync with this one, I'm going to close this topic to further updates. Please carry on with the new topic Alex has linked to above.