That trains is listed as "mandatory" because you probably have a discounted ticket, and the conditions of that ticket require you to take that train. This as opposed to flexible tickets that you can use on any train without much fuss.
But if you miss a connection due to a delayed train you are allowed to take the next available train (usually only from the same operator, unless there is an agreement in place) towards your direction. You should not have to pay extra because the railways messed things up.

So if you miss the connection due to a delay it is the railways problem. Normally I would expect this to work though. The conductors will normally not start the departure procedure until everyone has made their transfer.