Are the grains that I have been using with the Nik Collection for many years still available? Can I still use my presets?

Yes, these grains are available and all the previous presets are unchanged. The presets still feature the same film type and same grains if they previously did. All previously created presets from previous versions Nik Collection by DxO are going to be migrated to Nik Collection 4 by DxO.