I don’t think they would kill off Robin for good for the fact that if they do, Regina will have to end the series single. Regina is a character that loves deeply, she mourned Daniel for 30+ years after his death. Robin is supposed to be this big “OMG Regina has found love again!” For Regina to just move on from Robin with someone else would be OOC and realistically, the show is probably not going to go on beyond the next season, 7th at a push but that is very dependent on if they can get the likes of JMO and RC to continue by telling them it’s the very last season. Losing RC after the 6th as he has indicated that will be his last would be a massive blow for the show.
Anyway these are the likely scenarios I can think of in no particular order.
1 Robin dies, stays dead, and Regina ends the series single.
2. Robin dies, but Zelena makes a deal with Hades that she takes Robin’s place so she can be with him forever with the caveat that she can go to Storybrooke every now and then to see her daughter. (This makes Zelena Persephone)
3. Robin dies, Zelena agrees to take his place so she can be with Hades but her daughter gets to visit her for six months of the year. (This makes baby Hood Persephone)
All magic comes with a price!
Keeper of Felix