I generally keep a daemonized emacs or two running the entire duration of my uptime. If package A depends on a certain behavior of package B (but doesn't eagerly load it), if I start emacs, load package A, wait some duration X, package B gets updated, then I load package B, will A break?
If so, is that a failure of A for not eagerly loading B, or a failure of the dependency system for not letting A declare that it wants a particular version of B, or something else?
Sorry, I have not really dived into package.el all that much and the documentation is somewhat fragmented since everybody customizes it the way they want.
I remember a few elisp level error after upgrades.