Yes this happened to me. The battery light started coming on intermittently (and I posted about it here) and over a period of a few days the light would come on and stay longer before briefly going out. Only one dealer around so I had to wait a few weeks for an appointment, I still drove it in the meanwhile and put over 500 miles on it. Only after 3 weeks and several hundred miles the battery started showing signs of trouble: while on the highway on my way to the dealer the car shut down the tire monitor to save battery power (you get the yellow tire warning light). Next would have been the 4x4 system, and so on. The car is intelligent enough to start shutting down electronic systems starting with the least important ones. These are telltale signs the battery is dying and that's when you absolutely should not be driving the car.

So yes it's possible to drive a while provided that the alternator is still partially charging the battery, but there is no way to know that so it's better not to risk it.

Assuming you have the high-tech cluster, you can also check the voltage of your battery by pressing the right button in the instrument cluster that shows "CONTROL CHECK OK". keep pressing it for 10 seconds and you'll get TEST NO. 1. press it again until you reach TEST NO. 9. Then press the LEFT button (the one that resets the odometer). You'll get a live voltage reading which under normal circumstances should be in the high 13.x low 14x. When I had my problem I was in the low to mid 12.x volts. The reading will stay there until you turn off the car.

In my case it was the alternator and since replacement no problems.

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2006 BMW X5 4.8is (current)
2006 BMW Z4 3.0si (current)
1992 BMW E30 325i cabrio M-tech (RIP)