Since I had crash with my RPI, I am restoring my openhabian back again. Unfortunately I could not find the place where the customized widgets are stored.
I know the initial happanel page is stored at the following location:
I would guess that custom HABPanel components are also stored in a JSONDB, so my guess is that there is another file in the $OPENHAB_USERDATA/jsondb/ folder with habpanel in the name, but that‘s just guessing. I am not using HABPanel anymore, sorry.