The title asks whether a landlord can
prohibit subleasing; Tex..
State law
prohibits subleasing without landlord's consent, which makes perfect sense as per the above point.
Not exact matches
However,
subleasing is also
prohibited by most agreements, and only lease reassignment is generally offered, but then this does seem to be quite in violation of the damage mitigation statutes as per the specific example in the original question.
If the lease said, «any lawful use» was permitted and the property was zoned for either commercial or residential use, hiring an employee to be on the premises wouldn't violate either, even though a true «
sublease» might still be
prohibited.