Meaning of Lane lamps / lights being on

Land at the next airport that's practical for you. A lane light on solid is basically the same as a single failed magneto in a carb engine except unlike a carb engine, you know in flight that it failed instead of at next run up when you do a mag check. You lose redundancy but engine failure is not imminent because you still have one good lane. In theory you could keep flying forever but then if the last lane fails instead of just a lane light turning on the engine will quit.

If a lane is not working then it won't be any worse on your gearbox and you shouldn't just clear it unless you are troubleshooting because that just hides the problem. The working lane will take over the functions of the failed lane and the engine might run a little rich because it reverts to a "safety" mode where it only relies on necessary sensors like the crankshaft position sensor and ignores sensors that are needed for optimizing fuel economy. But it is no worse on the gearbox and there will be no vibration because the working lane takes over 100% of the functions of the bad lane.

I don't know why Rotax doesn't document these things more directly. People have noticed a pattern of poor documentation for iS engines.