I would like to know if the October 2019 switch from salesforce classic to lightning. Will the force.com pages stop working?
No. The change from Classic to Lightning only affects internal users, and not Communities and other external-facing technologies. Visualforce is still a supported technology and will be for the foreseeable future. We will not be forced to switch to Lightning Communities, etc for some time. Removing the Classic interface is a decision to reduce development costs and expenditures, allowing more resources to be dedicated to new features.