There are other threads on a potential third season but they are closed. This one though I think I'd like to focus on WHY I think there should be a final or third season...
The first main reason is that the second season was left wide open! I hate it when you get into a series and it turns out its an incomplete series!
Spoiler Alert: As to "would the main character be able to revive the fallen sekirei? I believe so, that was why in part they went to the MBI tower to begin with! I think that's also why they made a point of showing off the contents of those jars in the end of Season 2. I also think that if something was saved from them, then it would be possible to return them as full fledged sekirei! It really wouldn't make sense to bring them back as humans.
Potential Spoilers: This brings us back to where could they do this? If indeed they do return to the island, it would make sense that the only facilities left where they could be revived would be on the ship. Assuming there weren't other facilities built elsewhere. But what I have heard elsewhere is that the plan was to bring the masters back to the island with the crashed ship anyways, it would then make sense that there would be something there that would allow them to do so! They alluded to the possibility in some of the episodes of being to revive those that have fallen.
Here's an afterthought These beings sent eight ships to Earth in the past... Assuming that the original race is still around "out there" what's to say that they wouldn't come back to Earth to find out a progress report of what's been going on here? And who's to say that they wouldn't be pissed that some schmuck madman has taken over their projects for his own enjoyment? Course there is also the other side of it, what if they DIDN'T have benevolent reasons for sending the ships to Earth? Or at least that some other faction that may come into the Earth's realm of space may have ulterior motives? Why exactly DID the ships crash? Maybe these are questions that the manga answers, but I've only seen the show.
If there is a season 3 or final season, I would like to see another ship arrive to give their judgment on the mad scientist fellow! There would be bitter sweet revenge if the creatures/people/beings that sent the ships in the first place saw to it that their technology could not be missused, or would at least have something built in if things didn't go according to plan...