"It depends". The full facts must be analyzed, along with the text messages. The landlord should consult a landlord-tenant lawyer in his state.
The landlord should have prepared an updated lease and had it signed by the tenant. Trying to prove that the tenant agreed to that change based upon text messages is not going to be easy, and it probably isn't worth the investment of time and energy (and possibly legal fees) over a month's rent. Further, in most states the landlord needs to make a reasonable effort to find a replacement tenant and, with reasonable diligence, can probably find a replacement tenant by the end of the single month's notice.

