If a landlord asks a tenant who signed a 12 month lease to sign an addendum after they have already moved in that changes the terms of the lease to move out within 3 months of the landlord's death, and receive $5,000 for the inconvenience of moving out, is the tenant obligated to sign this addendum? Also, let's say that the addendum was originally referred to as the "garage lease" but became the addendum when it specified changes to the original lease. The rental is hypothetically in Chicago, Illinois.
You are never obligated to sign a contract. You already have a lease agreement in place, which will be enforceable for the agreed-upon duration. The lease can be changed if both parties agree to it, but one party cannot unilaterally demand that other agree to any changes to the contract - a landlord can't, for example, change your lease agreement to increase your rent payment in the middle of your lease term and demand that you sign it. The landlord is certainly allowed to ask, in the hopes that both parties can come to an agreement, but again, both parties need to agree in order for an existing contract to be changed.