I am always logged in. No, you can not save a draft. And yes, I lost a couple of draft posts too, for a number of reasons: I pressed a wrong button, something timed out, gremlins, etc.
Several ways to deal with it:
1. The one I use most often: if long post, I often Cmd-C on my Mac (copy to clipboard)... that way, if lost, I just Cmd-V (paste/insert from clipboard)
2. Use an external editor for really long and important posts, then just copy here
3. If no external editor available, you can always use Messages on this site to draft it, frequently saving it as per #1 or by sending it to yourself