The bus route Lijn 100, known to the database as relation #5719299, has been discontinued. There is no Lijn 100 anymore in that area, and the new buses follow different routes.
(a) use deletion: delete that route_master relation and the two route relations that are its children, as well as any busstops are no longer used as such; or should I
(b) mark the route as cancelled: change route=bus to route=disused_bus, as somebody once suggested in 2011?
When a local bus route was dropped in my area, I deleted the master relation, the two route relations and then looked at all the bus stop nodes they used. By survey I knew they left the benches in place, so I changed the former stops that had benches to amenity=bench. The stops that were only marked by a sign (now removed) I deleted.
I guess if there is a chance that the route might be reinstated with all the particulars exactly the same, it might be worth leaving the route in the OSM database. But mostly I think it would just be noise that may confuse or make issues when someone needs to split, delete or otherwise change some of the road network the route formerly used.