Generally with an assignment of the lease, the original tenant remains primarily liable for damages to the unit under the conditions of the original lease. The new tenant is secondarily liable. And the new tenant is liable to the landlord for all obligations under his lease (rent and utility costs, etc).I am sorry, I cannot seem to understand what you are trying to say. Did you mean that by default the subletter takes over all rights and obligations of the original tenant unless there is some agreement between them?
The original tenant’s security deposit (which appears to now include an additional $450) will cover damages to the unit but, should damage costs exceed the amount of the original tenant’s deposit, both the original tenant AND the new tenant can be held liable for these excess damage costs - absent any agreement to the contrary.
It is common for a landlord to draft a new lease for a new tenant even when the new tenant is taking over a lease from an early-departing tenant. The landlord wants the new tenant informed of all terms and conditions.
It would be less common for a landlord to release a departing tenant from his obligations under the original lease. The original tenant and the new tenant generally will be held jointly and severally liable for the condition of the unit for the full term of the lease.