The best and most credible way to realistically bring Stephen AND Cutter back would be a story line that shows the vies how both characters (the dead ones) were actully clones and the REAL Stephen and Cutter were lost in another time anomoly...this way their character and their personalities, memories etc would all be intact. 

The history will have a recap showing how Stephen and Cutter were somehow manipulated by Helen in Series 2 (unknown to the viewer) and kidnapped & replaced by their clone counterparts.  There could be an episode where we have a flash back in Helen's mind thinking of Stephen and Cutter and how they were forced into an anomalie and replaced by their clones so that Helen could get them out of the picture without actually hurting them (she really does care about both of them...so we can see the "tender side" of that witch... 

Then we actually see Stephen & Cutter, alone in some prehistoric or future era....hiking along jumping into yet another anomalie trying to find home and....viola!  they finally make it home only to find that everyone thought they were dead but now alive...every one is happy....the boys have a new contract with the show....and the show will be now be better and we can all go on enjoying the original reason why we started watching this great series with 2 really awesome characters that should have never been killed off.......People, people. people.....America is just getting this show...you can't let Cutter or Stephen get axed off the show!!!