The railways in Germany are very good in offering alternative transport if the train you have planned to use can not be used for whatever reason.
First thing to do, ask any person sitting near you to explain, if they can. Next look for a person in an uniform. And if non is near, go to the ticket office in the station you are.
The uniformed staff or ticket window staff will tell you which train you can best use, sometimes giving you an alternative route.
You may not get a reserved seat on the alternative route, as that can not always be arranged, but in first class you can almost always find a seat or ask the train staff to help you find one.
I have had the same kind of problems several times in Germany, always got to my destination on the same day, if a little later than planned. And at no extra cost.
If your delay make you miss your last train of the day, they are supposed to help you reach your final destination that same night or put you up for a night, but you will have to ask uniformed staff or ticket office staff as soon as you have a reasonable expectation of that happening, to allow them to arrange things.