Often people get confusing messages from the railway (the Railways are good at this, DB being the undisputed champion here) and get a bit in an unnecessary panic.
What you have to know is this: You have not bought a train ticket. There is no such thing as a train tickets. Train tickets do not exist. Railways will not sell you train tickets.
What you have bought is a ticket for a route. Eg. You may have a ticket for Vienna - Prague. And you probably did select a train during the purchase process. (That is relatively new, I can still remember that all you needed to enter was origin and destination). And you may have obtained a discount that is conditional on trying to take that train you selected.
You may also have bought a reservation. That gives you a seat on a particular train.
Now it is possible that for some reason the train you wanted to take is not operating. It is for this reason that railways always tell you to check the actual schedule on your day of travel. Things may change. And in Austria, (as well as eg. in Germany or Switzerland) if a train is cancelled all you do is just take another train on the same route. You do not need to have your ticket changed for that, as it is after all not for a train, but for a route. So as long as you stick to the route on the ticket you are fine.