My opinion is that if the controller was fired as a result of this incident, the ANSP has a poor safety management system which will result in more incidents such as this one, or worse.
Callsign confusion is an issue that can be addressed in many ways but at the end of the day it will always exist. For example, yesterday I had an Easyjet aircraft take the call for a Ryanair aircraft with a completely different callsign. What can you do in such a situation? My thoughts to mitigate against further occurrences would be:
Controller training - Making controllers aware of callsign confusion and the associated traps.
Operator cooperation - Getting operators on board to help avoid putting very similar callsigns out there at the same time.
Technology - It doesn't look like it but does the equipment provide any sort of data link via Mode S or ADS? Such information paired to the right systems could help nip such a problem in the bud. Was there any form of conflict alert to make the controller aware of the potential and actual loss of separation?
Aircrew training - Making aircrew more aware of callsign confusion and the associated traps. Possible CRM issues too?