No way Heathrow is coming back unless there is a 3rd runway. Even then, there has to be enough demand from a combination of direct traffic to/from London (so against the train) and connecting traffic (against KLM to AMS).
For connecting traffic, I think the problem for FlyBe/Connect is that Virgin does not have anything like the route network out of LHR to feed that BA does. FlyBe do not seem to have made much a success of offering codeshares to mainline carriers and even if Virgin/Connect was to join SkyTeam, you couldn't really fly that many extra places via LHR that you couldn't via AMS today.