I've had a CEL on in my car for the longest time for a secondary o2 that I'm too friggin cheap/lazy to replace the only thing I've noticed is that it's a little harder on gas than normal. With it being made by Toyota I honestly wouldn't worry about it.
well first of all I'd say have you pulled a code to know thats why the CEL is on? and if it is an o2 fault then yeah your fine most likely will just run rich and use up some gas 200 miles is no biggie. Long term could burn up cat fill everything with carbon deposits but that would be thousands of miles.
Lexus will drive fine. Limp mode is rich; but its not as super rich as everyone is describing. You can drive a Lexus into the dirt and it will still run. Don't worry about it, but replace the O2 sensor soon enough.
I ran my SC300 on limp mode on purpose when it was turbocharged because it ran a little extra rich and less timing. He'll be fine and it won't damage a thing.