I've had an alternator go twice on my focus. The first time, it just refused to start the day after the whining began, but the second time the power steering cut out, loads of warning lights came on and then everything went dead. Speedo, lights, not even the hazard lights came on, and I had to push it to the side of the road and wait for the AA.
If you have a multimeter, check the battery. It should be about 12v or so with the engine off I believe, and it should be around 14 or so volts with the engine on. If it's any less than this, or it doesn't go up with the engine running, it may be the alternator. It will be safe to drive, but beware that you may lose ALL electronic driver aids (my power steering went half way round a corner, and it caught me off-guard. Could have been VERY dangerous) and may get loads of warning lights flashing up on the dash (my handbrake warning light came on at 50mph!).
This may not happen immediately - mine lasted over a week from the whining starting to the problems happening.
Hope this helps and that all is resolved ASAP .