Indeed, it means that on that day, the train will not run as usual. However, only a portion will be different.
The ICBrussels train runs between Amsterdam and Brussels, through Den Haag and Roosendaal. According to the message you saw, your train will run only between Roosendaal and Brussels. You will have to find another way to go from Den Haag to Roosendaal.
While the interruption is not shown on the works interruptions page, you can see what is expected from travellers. It suggests once to rely on the national trains. However on the national trains website, it also mentions the works and recommends to take the bus, but it says the advice is not yet final (I used Google translation, so someone could be more precise on that part). And it recommends to plan at least 10 days ahead.
So you have 2 options: take the Thalys, more expensive but a priori not using the same tracks on that itinerary, or coming back later on the train website (the price does not seem to change) and plan ahead. It does not say precisely how the bus will work (and if it is a specific shuttle or an existing line), but I suppose you can expect to take a train from Den Haag and Dordrecht, then a bus from Dordrecht to Roosendaal, and finally the ICBrussels from Roosendaal to Brussels. Expect some delays, so take your time, if you go that way. But in any case, you should be able to reach your destination.