They can always turn the machine back on, plus Olivia just needs to think really hard to go back and forth at will... Not to mention there is the portable device that the bad guy uses to move around himself.
I suspect the end of the series will be working on the Observer's takeover, trying to prevent or prepare for it.
I suspect the same thing.
OF course in the Crisis on Infinite Earths in Dc comics back in the 80s (similar plot -multiple universe earths ) the last two earths in the universe merged and all the people on both earths were integrated into one earth with a new background history. The super heroes on the last two earths left traveled back to the beginning of the universe and destroyed the Anti-monitor, who was trying to destroy all the multiple earths in the multi-verse. The super heroes that were left in from the beginning of the universe time ,remembered their back grounds before the change and the rest of the heroes left in the new integrated earth ,didn't remember their lives or history before the integration took place.
So they could integrate the two worlds in "Fringe" and the remaining characters could be all included on one earth with a common history. One Oliva with both the hot hair color and fiery personality ,but with the other's sensitivity and love for Peter. The two Walters could be integrated with both genius like nutty Walter ,but with sanity, confidence, etc. , like the other earth's Walter. One world with both high technology like the other earth, but not dieing or being destroyed from the "fringe" occurrences.
So if they wanted to they could some how cause the integration to occur using the machine,without destroying the worlds by synching the two earths to a common vibration pattern , like Walter alluded to in last night's episode. I'm betting that some how this will be part of stopping the Watchers take over of the worlds. In the end you end up with one world , with a common set of characters representative of the best of both worlds with no memory of how the world was before the integration , the watchers destroyed or they never existed because of Walter's use of the machine with Peter . Basically the entire show never happened the way we saw it ,because time was changed, along with the multi-verse being changed to one universe.
Now lets see if they steal this ending of the show , just like they stole my ending for Battle Star Galactica. I wrote the ending for that show a year before it ended and they took it almost word for word the way I wrote it. So next year at this time lets see if they took my Fringe ending too.
