On the UV editor you can enable "Sync UV and Mesh Selection". However, I rarely have this enabled while UVmapping because I've never felt it to be necessary (I don't see the point of why you need to see the UVmap while selecting faces actually). Even if it's disabled any mapped faces will stay where they were when you previously unwrapped them unless you remapped them. They don't actually disappear. I only have it enabled if I need to see which parts of a mesh in the 3D viewport belong to which part on the UVmap. But for unwrapping purposes I always have them disabled by default.
My usual method while UVmapping is to put all the proper seams on the model and then unwrap all faces at once. Afterwards I just rearrange/rescale/reshape the UV islands accordingly. If I need to remap certain faces again I just pin the faces I don't want to remap first (select the faces on the UVeditor and press P), and then on the 3D viewport I can select all faces and unwrap again, any pinned faces will not be remapped while unpinned faces will be remapped accordingly. An exception is if I want to use Project from View or other UV calculation methods. In those cases I will select only the faces which I want to apply the UV calculation on before applying it, all other mapped faces will not be remapped (if you had them selected, they will be remapped even if you pinned them).