I'm a relatively new pd user
I had an older version of pd, and I was encountering weirdo technical problems, and in a fit of panic I threw out all versions of the application and its libraries and downloaded the latest version of pd-extended.

However, on running pd-extended 0.43.4, many included libraries were listed as "unable to connect", and a number of the objects I was accustomed to using were not usable (e.g. expr, delwrite)

I was used to pd loading an external "library" folder with many of these external libraries included. can't find that neither.

perhaps this is a problem with my sleep schedule.
anyone wanna help a scared child?

Yop,

this should help : http://puredata.hurleur.com/sujet-8112-install-externals-libraries-gui-plug-ins-etc

so I deleted my copy of pd along with its library in a fit of mania before downloading the latest version.
now, there is no ~/Library/Pd
nothing in my library related to pd neither.

did I fuck it irreparably?

No. By default, there is nothing in ~/Library/Pd. That's just a folder used to add libraries that are not included in the distribution. You don't really need it if there's nothing in there.

It's possible that your new install is using the old preferences. See here to fix that, if that's the case:

http://puredata.hurleur.com/viewtopic.php?pid=35138#p35138