Locating TERA install if upgrading to EME Launcher (Updated)
This came up in Discord so I wanted to make a post here just in case.
If you are still using the old TERA Launcher and need to upgrade to the EME Launcher, after you're finished installing the new launcher it will ask to locate your current TERA install folder. The folder you need to choose for this to work is the subfolder called "Client" inside your current "TERA" folder. Don't pick just the "TERA" folder (where the old launcher is) because it won't work; expand the TERA folder and pick the one called "Client". Then it should detect it and allow you to run without reinstalling (although it might ask for an update).
Hope this helps someone avoid an unnecessary reinstall.
(Edited for clarity.)
It seems that if you follow the forced-upgrade process inside the old TERA Launcher, it says that it will uninstall the old TERA Launcher, and it's as part of this process that it can delete your old TERA install. So the way around this is, instead of doing the in-place upgrade when prompted, instead just download the EME Launcher directly from the web:
After installing the launcher separately (without going through the upgrade process), then you'll be able to simply link your existing TERA install and keep playing from there. The instructions above about finding the Client folder will apply.