Lenny
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It's still up in the air whether Fringe will be renewed, because at this point, the only viewers are the hardcore fans - despite the writer's best efforts, they've not been able to tempt new viewers to watch the latest series. Because of this, another series will most likely be it's last, simply to allow the writers to put together a proper ending to satisfy the fans (it would also give Fringe a total run of just over 100 episodes, which always looks good).
There have been quite a few efforts from Warner Bros. to make Fringe more appealing to Fox, including lowering the licensing fee Fox pay them to show the episodes, which ups it's chances of being renewed. It's also helped in part by the terrible reception Alcatraz got (which is a shame, because that's also a good series) - as a result, it's highly unlikely that Alcatraz will be renewed, meaning there's space in Fox's schedule for Fringe.
So, it's likely that there will be a fifth and final series, but just in case, two endings to this series have been filmed - one with a lead in to series five, and one that ends everything nicely.
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Regarding Leonard Nimoy, I seem to remember reading that he was only contracted to physically appear in four or five episodes. Obviously, his character has technically appeared in a great number more, but he himself will not be returning. However, I wouldn't say the character is completely gone (indeed, Nimoy's likeness was in the amber, probably through some CGI trickery), particularly not with everything we've seen in Fringe regarding alternate realities, shapeshifting, body-snatching, and time-travelling.
If William Bell turns out to be Mr. X, then it will probably be a different version of William Bell to the one we know as Leonard Nimoy. He may appear to be in a new body (we're told a few times that William Bell died in a car crash in the red Universe... but what if it was simply his body that died?), or a much younger form of himself may appear. Heck, what's to stop a cloned version of an earlier form of William Bell rearing it's head? After all, the cartoon representation of Mr. X in the LSD episode did not resemble the present version of William Bell.
Obviously, it may turn out that William Bell is not Mr. X, and that the man himself is someone completely different.
Assuming the future in which the Observers invade is the future for the current timeline (indeed, as beings that aren't constrained by time or reality, it could be that the Observers invaded every single possible timeline in 2015), then we know that William Bell does something to Olivia that means she wasn't ambered along with the rest of the team in 2015 (Walter's exact quote when talking to Astrid is: "You remember what he did to Olivia. Even you can't be that compassionate", implying something truly terrible). It's more likely that William Bell is the main antagonist if there is a fifth series, with Mr. X working for him, than Bell being Mr. X, but either way, I think William Bell will be featured quite heavily in the next storyline.
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If this does end up being the final series, and the finale to end it all is aired, then I wouldn't put it past David Robert Jones to be Mr. X. With enough plausible explanation, it could work, and it would tie up a thread nicely.
There have been quite a few efforts from Warner Bros. to make Fringe more appealing to Fox, including lowering the licensing fee Fox pay them to show the episodes, which ups it's chances of being renewed. It's also helped in part by the terrible reception Alcatraz got (which is a shame, because that's also a good series) - as a result, it's highly unlikely that Alcatraz will be renewed, meaning there's space in Fox's schedule for Fringe.
So, it's likely that there will be a fifth and final series, but just in case, two endings to this series have been filmed - one with a lead in to series five, and one that ends everything nicely.
---
Regarding Leonard Nimoy, I seem to remember reading that he was only contracted to physically appear in four or five episodes. Obviously, his character has technically appeared in a great number more, but he himself will not be returning. However, I wouldn't say the character is completely gone (indeed, Nimoy's likeness was in the amber, probably through some CGI trickery), particularly not with everything we've seen in Fringe regarding alternate realities, shapeshifting, body-snatching, and time-travelling.
If William Bell turns out to be Mr. X, then it will probably be a different version of William Bell to the one we know as Leonard Nimoy. He may appear to be in a new body (we're told a few times that William Bell died in a car crash in the red Universe... but what if it was simply his body that died?), or a much younger form of himself may appear. Heck, what's to stop a cloned version of an earlier form of William Bell rearing it's head? After all, the cartoon representation of Mr. X in the LSD episode did not resemble the present version of William Bell.
Obviously, it may turn out that William Bell is not Mr. X, and that the man himself is someone completely different.
Assuming the future in which the Observers invade is the future for the current timeline (indeed, as beings that aren't constrained by time or reality, it could be that the Observers invaded every single possible timeline in 2015), then we know that William Bell does something to Olivia that means she wasn't ambered along with the rest of the team in 2015 (Walter's exact quote when talking to Astrid is: "You remember what he did to Olivia. Even you can't be that compassionate", implying something truly terrible). It's more likely that William Bell is the main antagonist if there is a fifth series, with Mr. X working for him, than Bell being Mr. X, but either way, I think William Bell will be featured quite heavily in the next storyline.
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If this does end up being the final series, and the finale to end it all is aired, then I wouldn't put it past David Robert Jones to be Mr. X. With enough plausible explanation, it could work, and it would tie up a thread nicely.