Yes, Soyuz spacecraft can serve as a lifeboat and return a single crew to Earth. From Anatoly Zak's Russian Space Web page:
In case of emergency on the station, the Soyuz can be sent up unmanned
or piloted by a single cosmonaut to serve as a lifeboat; or be used as
an unmanned cargo ship to return 250 kilograms from orbit.
If for some reason contact with ground control is lost, vehicle can't use ground-based telemetry for guidance, or its autonomous flight mode failed, it will default to a high g ballistic entry. This means it will likely miss its landing site by quite some margin, but it has happened on several occasions before. Soyuz TMA is quite a robust crew return vehicle. Refer e.g. to James Oberg's Soyuz Landing Historical Reliability Study for more details, it sounds nearly impossible in what all circumstances Soyuz managed to return crew back home alive, though deadly accidents during deorbit burn and landing did, sadly, also happen.
As for post landing support, well, if there isn't anyone left to await the returning single person crew and thus no recovery forces to meet him or her at the launch site, that kind of forfeits any physical therapy and post-landing support, too. That person is forced to manage on their own.
With a bit of luck however, depending on when the emergency happened, that person wouldn't have been on orbit and in microgravity conditions for a very long time. Deorbit burn will have to happen in up to 200 days after Soyuz TMA was launched into orbit, since that's it's maximum on-orbit standby time. A single crew without all the Mission Control Center's flight controllers keeping an eye on all the sensor readings is also unlikely to maintain the station safe for a very long time, so it would have to be evacuated pretty much the same day as the emergency scenario happened. It also depends on each individual how adverse effects of a prolonged stay in a microgravity environment will be, and how fast they acclimate back to Earth gravity conditions.