Each form of a lexeme must have at least one representation, and each sense of a lexeme must have at least one gloss. This is currently enforced only by the API:

We see two options to prevent this in the UI without showing an API error: we can disable the “save”/“publish” button if all representations/glosses have been removed, or we can disable the “remove” button on the last representation/gloss when there are no other representations/glosses.

Disable “save”/“publish”:

Disable “remove”:

WMDE-Design what do you think? Lydia is ok either way (see T198035#4436197).