I think it's a pretty modest risk. BRS-BRU has operated for years, and survived the Sabena fiasco, so I assume it's basically profitable. Brexit is certainly a risk though.
virginblue: BRS-BRU was the only route operated by a Star Alliance airline, so after 29OCT there won't be any more *A traffic to BRS. SN and LH will continue to codeshare on the BRU/FRA/MUC routes, and issue tickets across them, but it will be outside the *A network.