Me and my friend were on a train to Brussels on the morning of the terrorist attack in 2016, on our way to Bruges. Needless to say our train was cancelled in Liege as all traffic in Brussels was halted, but we were able to take alternative route via Antwerp and proceeded with our trip as planned, spending a few days in Flanders. It was pretty much business as usual and the most memorable thing about this trip was reading my local news websites which made it seem that the life in Belgium almost stopped, while I was sipping beer on a terrace and had a square full of people hanging out in front of me (and no, it wasn't just tourist areas).

The only thing we changed back then is that we removed a day-stop we had originally planned in Brussels three days later on our way to Luxembourg. But we still had about half an hour to change trains there, and when we went out of the station for a bit, it seemed that it would actually be pretty ok to do that stopover. There was heavier police presence but that was it.
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And those were major terrorist attacks by large organised groups, not some lone wolf. If I were traveling to Brussels today, I'd expect to be completely unaffected by this incident.