I'm in the same boat now. I have a ZRH-ARN on 6th April and the flight no longer appears on ExpertFlyer, it's the last leg of a ARN-ZRH-SIN-AKL-SIN-ZRH-ARN trip, I looked on FR24 and the last listed flight for that city pair is the 13th March then nothing. I leave AKL on the 31st March and have a 4 day layover in SIN before the SIN-ZRH-ARN legs. I also have a trip onwards from ARN-LHR on BA so it would make sense to change the ZRH-ARN leg to ZRH-LHR (which means I'd have to cancel the BA flight) but I guess I'll just have to wait and see what pans out. This was an ex-EU trip and the BA LHR-ARN-LHR is a separate PNR so getting into ARN on any other flight means I will miss the connection as I only have a 2h 40 min connection time.