learning that arch immediately purges the files of the running kernel makes me feel things.
you do not want to do this as your kernel is usually built as modules. so if you add a new device, the kernel may want to load a new module from disk. but arch replaces the kernel immediately.
until yesterday i was not even aware that this could be an issue. and other distributions like openSUSE and Fedora it is not. and i found a suse forum entry from 2011 explaining how the kernel purge rules can be configured. you just keep the previous kernel installed is the answer and especially the running one. this is also possible as the module folders and similar all versioned with a symlink always pointing to the active one.
the old one also shows up as a boot entry so going back when there is a bug is trivial.

a 2013 arch forum thread just says that arch does not do this and only keeps one per package type and deletes the old kernel and its modules immediately.

incredible how old arch problems, other ones i recognize from daily using it in 2014-15 are still around today...

my personal respect for arch decremented yet again