Semira isn't actually deadSemira is stabbed through the back of the head which apparently kills her. However, at this point, she was a Vampire-Corvinus Strain Hybrid who have been shown to have equal, or even superior, power and strength to the Elders. Previously, Viktor survived virtually the same injury; therefore, unless they torched her body then Semira surely could've survived such an injury as well.
Semira was Viktor's protégee.But he sent her away in favor of Selene, due to her resemblance of his daughter. Possibly in his last moment, Viktor was thinking of Semira.
- Semira herself has a slight resemblance to Sonja (they're both pale and dark-haired), Semira was said to have been his regent and clearly held Viktor in a high regard. She also appears to be jealous of Selene and is resentful over her killing him. It would therefore be plausible that Viktor regarded her as a protégee of sorts, but ditched her in favour of Selene.
Michael isn't actually deadThe only source to confirm that Michael is dead is Marius's blood memories, and it may be that Selene only saw part of those memories, or Marius was unaware of the scale of Michael's regenerative abilities and he would eventually recover from the implied bloodloss unless they actively destroyed his body, which they would have had no reason to do.