Check with your airline. But what tends to happen is that long haul flights are given priority over short haul when mass diversions take place. this should mean that you're ok for the United flight, but there is a chance that the flight to Germany could be affected. Chances are that if your connecting flight is cancelled you'll be offered a different flight or they do sometimes offer other means of transport, such as Eurostar to France/Belgium and connecting train/flight from one of those countries. If there is a delay, and the second flight is with an EU based carrier you are entitled to compensation from that airline for reasonable expenses incurred by you (food, accommodation etc) under EU regulation [EC]261/2004 (though you must keep all receipts and it does involve a lot of paperwork, and the airlines aren't particularly happy about it). No matter what happens, though, the EU airlines do have a legal obligation to get you to your destination or as close as possible so either way you should make it.