Most (if not all) airlines do not use those numbers again until the incident is all but forgotten (a few decades later!). I dont think they do it to respect the victims but rather for PR
reasons (who would want to sit on SR111 that crashed yesterday ...)
Swissair did change the flight number SR110/111 immediately (cant recall to what though), as did Singapore Airlines (SQ5/6 to SQ29/30)
Best Business Class: Royal Brunei. Best Economy: Singapore Airlines. First: please send money first!