As a seller, you HAVE TO and should declare anything that would materially affect the value of a property aka a fire. In your position, I would make sure to disclose the fire issue while also providing documentation regarding proper remediation and replacement. I probably would not replace the rest of the roof and, if a buyer wants a new roof prior to closing, I would address it then. However, some buyers may be turned off to a partial replacement because of aesthetics or just bias. That is something to consider as well.
Lenders generally do not care about the condition of a roof unless it comes up in the four point inspection or appraisal. A failed four point means a purchaser cannot obtain insurance. There are ways around that if your insurance agent is creative enough.
