A website that is still up proves nothing. Domain names keep renewing for years and a LinkedIn page rarely disappears by itself. So look at the company.
The three sources, in this order
1. The Crossroads Bank for Enterprises. Says whether the company is still active and, if not, since when it was ceased or struck off. This is the fastest check and needs only the company number.
2. The Belgian Official Gazette. Says what happened: a merger, a name change, an acquisition, a dissolution or a liquidation. This is the source with the story attached, and that story determines what would happen to your contract or your work.
3. The most recent filed annual accounts. The year is a strong signal. An agency whose latest filing is three years old is not active in practice, even without a formal cessation anywhere.
The trap in this question
Relying on one source does not work, and the error always runs the same way. A search returning nothing reads as "all fine", while it can equally mean the company is gone. So always confirm a suspicion with a second source.
Three states that are not the same
- Absorbed. The agency was folded into another; the people and clients usually continue under the new name.
- Ceased. The company stopped with no successor. What remains of the work depends on your contract.
- Dormant. Not formally stopped, but without activity and without a recent filing. This is the hardest state to establish and the most common.
What the factsheets do
On the factsheets, an agency absorbed into another keeps its page, with a notice on it and a pointer to the successor. That page is deliberately neither redirected nor removed: the question "what happened to this agency" deserves an answer, and a 404 is not one.
See also: who owns an agency and how to know whether an agency is financially healthy.