"Fringe" is in a sci-fi class of its own. It is one of the few sci-fi shows that it based in reality. It doesn't involve aliens. It doesn't take place in the past or future. It doesn't take place on a spaceship. Basically, it is not the type of sci-fi show that is thought of as "nerdy" enough to be mentioned on "The Big Bang Theory." If it is at all possible for "Fringe" to continue (perhaps in an alternate universe), what should the show do to ensure its survival far into the future?
"Fringe" needs to continue doing what it's already doing.
"Fringe" is based on fringe science, but reaches far enough to the limits of believability (and often crosses that believability line) to be considered great sci-fi. If it was more in the range of believability, it would probably be liked by more people. The problem is that it would no longer be the same show.
If the producers, directors, and writers want to keep their current fan base and continue their strong legacy for years to come on DVD and in digital sales, they should continue in the current vein of the show. Any change to try to increase their viewership will be seen as selling out and will shatter the entire "Fringe" world. Sales would flatline, and fans would probably boycott.
It's up to the fans to keep it going.
The reason "Fringe" was able to get a Season 4 was entirely because of the fans. If "Fringe" is to get a Season 5, it will be because of the fans, once again. If it gets a Season 5, then the fans will simply need to continue pushing if they are to get anymore seasons beyond that. That may mean petitioning to get the show moved somewhere else, such as Netflix. The fans could also take Cortexiphan and create a future wherein "Fringe" is never canceled.
Can it find a home that will appreciate it for what it is?
The only other home, besides FOX, where an expensive show such as "Fringe" could possibly work, would be Netflix. It's possible that they would save the show long after cancellation, as they did for "Arrested Development." The fans will simply have to continue pushing for it after the show is canceled, without giving up.
The cast of "Fringe" can't give up.
Each actor on "Fringe" is perfect for the show. If the show were to be canceled and brought back at a later date on Netflix, there's no guarantee the actors would come back. They are all fantastic and would certainly move on to other projects. Unless by some miracle they are all free and willing to come back at a later date, the show should stay dead.
The most notable characters the show could not live without are Walter Bishop (John Noble), Olivia Dunham (Anna Torv), and Peter Bishop (Joshua Jackson). The show just wouldn't be the same without the others, however. Astrid Farnsworth (Jasika Nicole), Lincoln Lee (Seth Gabel), Broyles (Lance Reddick), and Nina Sharp (Blair Brown) are all very important characters. If at least one or two of them (played by the same actors, of course) were not able to return, the show would be difficult to resurrect.