Had a user that had loaded a family with a lot of types in it. He purged his project, but then discovered he needed one of the types he had purged. So, he opens the original family, and tries to use the Load Family tool on the ribbon, but he doesn't get the normal overwrite dialog (which allows you to either load just the family or load and overwrite the parameters). He also didn't get the original types reloaded into the file. His first thought was to just delete the part(s) and reload the family, but that added a lot of work.
At first I thought it was a bug, but the big man upstairs (my boss, Norb Howell) reminded me of a behavior in Revit. You only get the overwrite dialog if the original model has been changed or saved, since it's the date stamp that kicks this dialog off.
So how do you fix it? Easy - just open the original part and save it. You might have to edit a parameter, or make a minor change (better yet, fix something that's actually broken). Reload the file and you'll get all the types back.
Better yet, add the Smart Browser tool from AGA CAD (Tools4Revit) at http://t4r.aga-cad.com/Smart-Browser-download-page/. We love this app, it's a real time saver.
This add-on, which has free and pro versions, allows you to locate a family, and then load just the types you need, in the event a type catalog (.txt) doesn't accompany the file. You can pick and choose the types you want, and only load what's required. The same rule applies, but if you're thinking ahead and know you'll need more than one type in a family, it's a better way to load these to your project.
Check it out - happy BIM'ing!