Modern SID/STAR design has built in either segregation or separation assurance, and pilots are used to flying them (albeit for same runway, not for RRO). The safety issue arises when pilots start doing something what is not normal for them (the old fashioned radials, etc), such as NOT flying the SID/STARs that are already programmed into the aircraft and they are mentally attuned to using. The locals know which way the airline transport flights go but there's not many of the former overnight.
Lets just say that the QF used the RUSKA Six Departure RWY 11 and the Jestar was inbound on the VEGPU Seven arrival RWY 29 there is NO traffic separation provided by this SID/STAR. The tracks crossover between ITTSA- SARRE inbound and PAGSO-VABLI outbound whats more the departure is restricted to not above 6000 prior to VABLI while the arrival has to be below 8000 after VEGPU, further condensing the traffic into similar airspace considering the arrival is on a constant descent from VEGPU then it would probably pass very close to the departure climbing from 3000 to 6000 ft. These SID/STARs would never be used in actual combination without ATC restrictions. There is nothing on either SID/STAR that prevents the arrival and departure aircraft from being at the same altitude when transiting those tracks.
Hence these SID/STARs should not be used OCTA as pilots do not know what SID/STARs should be used in particular combinations. This is why controllers talk about runway configurations, it is referring to what is being used for arrival and departure paths and determines what SIDs/STARs will be used.
It is obvious that the RWY 29 RUSKA has a not below crossover to allow separation with inbounds to RWY 29. However OCTA an aircraft can choose to operate any runway it wants to, there is no runway configuration in place, so therefor the SID/STAR patterns are not going to ensure traffic separation.
Now what is the answer here, well first of all it needs to be understood when a SID/STAR will ensure separation, nothing in the documentation states that the RUSKA 11 and VEGPU 29 should not be used simultaneously. Remembering that a quick look has the departing aircraft turning at 900ft so it should be quickly out of the way of arrivals if they haven't started the ILS yet, but no, the conflict point is a number of miles from departure approaching the en-route phase. So an aircraft that is miles away suddenly becomes a conflict. None of this is saying that is what happened here, but it highlights how using opposite direction SID/STAR is not a good idea.