Good:

  git log --all --graph --oneline --reflog

Better:

  git config --global alias.lg "log --date=format-local:'%Y-%m-%d %H:%M:%S' --pretty=format:'%cd %<(20,trunc)%an %C(auto)%h%Creset%C(auto)%d%Creset %s'"

  git lg --all --graph --reflog

> Is it possible to get a true chronological log from them?

The output of git log with --graph is not chronological, because it does a topological traversal of the commit graph.

> Do they stay around forever or do they get garbage collected eventually?

They get garbage collected eventually. As a rule you should not assume dangling commits are safe. If you need to keep one, assign a trivial branch name to it.