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.

> What's the UI for getting at those old commits?

The same as any other commit. You can check them out by referring to their hash, by referring to any tags that point to them, or any branch that points at them.

The other reply gives options assuming the commits have been orphaned (no tags or branches point at them).