The guarantor does not have to be told of an assignment of the lease and it makes no difference if, by the time action is taken over unpaid rent, the guarantor has no association with the original tenant. That can come as a considerable surprise to some parties. To take matters to the point of absurdity, the guarantor also may be liable for the balance of the lease term, even if subsequent tenants are only liable for the time they hold the lease. That applies even if the guarantor has broken out of a partnership or sold its share in the tenant company. In addition, the guarantor will continue to be liable if the building changes landlords, unless the guarantee states that it is limited to one particular owner.
Landlords also have some restraints, although nothing as onerous.
A landlord who sells a building cannot sue a tenant for previous breaches of lease. They must rely on the purchaser to do that. Many sales agreements allow the vendor to sue in the purchaser's name for pre-settlement arrears. If that clause is not included, the new owner can still sue a tenant for breaches before the building changed hands. Tenants and guarantors should study carefully the wording of a contract about lease extensions.