As has been mentioned in this forum recently, the change back to SN flight code (flybmi had operated latterly under BM as a code share with Brussels Airlines) with AR8 aircraft (which some presumed at that time to be CityJet) from 31 March was shown in the Brussels Airlines booking engine as far back as last November, although I don't think an official announcement was ever made.
Had flybmi not ceased to operate as an airline in mid-February it begs the question as to whether the BRS-BRU route would still have ceased after 30 March.
On the Monday following the weekend news of flybmi's cessation the BRS CEO was interviewed on the local ITV News about the situation. He made the expected comment about the airport working hard to find replacements for the lost routes and went on to say that he was confident that there would be news later that week of one of the routes being taken on by a European airline. It wasn't Loganair to ABZ because that had already been mentioned. One assumption was that the news would be a confirmation of what had been in the Brussels Airlines booking engine since November. If the BRS CEO was alluding to the BRU route then something obviously changed during that week.