Regarding Rakheid, I have a theory. He is not actually real, but created by Mavis' subconcious through her illusions magic. Similar to Zera, but Rakheid is much more tangible in that everyone can see him, and he is more "physical". This may explain his immense strength (even blocking a sword with his fingers), because he has no physical limits unlike a real flesh and blood human.
It would also explain why August said Mavis (the mother) is the only one who can defeat Rakheid. Similar to Zera's case, if Mavis becomes aware that something her subconcious created isn't real, that entity will cease to exist.
My theory is when something traumatic happens to Mavis, her illusions magic triggers to create something from her subconcious. In Zera's case, it was when Zera died. In Rakheid's case, I suspect Mavis' own death is the traumatic event which triggered her subconcious to create something even more tangible and powerful than Zera; her son Rakheid.
Regarding Kagura, I don't think Kagura is dead. Firstly, it's Fairy Tail and it is very rare for characters to die. It would do her injustice to die like that. Secondly, Kagura was stabbed by Minerva in the Grand Magic Games arc, and she lived. You even got Gray and Juvia stabbing themselves just a few chapters back, and they lived. So, Kagura will live.