I was thinking about it and I feel like 4x06 would have been an interesting place to actually break up Caroline and Tyler after Dean’s (?) death. Like I love Caroline and her willingness to kill someone else's loved one in order to save her own. She's a girl who has proved her answer to the trolley problem at least three times on the show. But it's also understandable if Tyler was not cool with his girlfriend being complicit in his friend’s murder and this being something they can't move pass, for the time being at least. They still love and care about each other but it's not working.
This would progress things in potentially different ways. One it could potentially propel Tyler into being more involved in the season long arc involving Silas. He would become more isolated (sorry Tyler) and after Hayley betrays him and the hybrids get killed, Shane (and possibly Hayley) could appear telling him they know a way to bring them (and Carol) back. Tyler has no interest in the cure (other than giving it to Klaus possibly but that plan never made sense to me as it seems like a dead human Klaus would still kill everyone in his sireline including Tyler, but this could also be part of the plan) but he would have a huge desire to save his pack and make up for what he would perceive as his failure. This season is all about the crazy things people do because of grief and lost family, why not include Tyler in that and let him be seen even after he leaves town as he works for Team Shane. Because the show had a terrible habit of giving him a good storyline in the first half or so in the season and then having him disappear in the second half.
On the flip side, as this season was trying to push Klaus and Caroline together more, an actual legit breakup would help with that. And when Caroline isn't in on the plan with the hybrids, Klaus can cherry pick the things about what happened he actually tells her. (Manipulation is bad yes, but also in character.) On top of that it can develop the Stefan x Caroline x Klaus dynamic they set up but didn't fully utilize, the three of them all wanting the cure for Elena for different reasons. Caroline fully throwing herself into the plan to avoid her feelings about the breakup makes sense. We could see her going to Klaus to find out as much as she can about the sirebond (saw a post where someone suggested this recently and I agree they should have used the older vampires for info more), as well as trying to get more information about Silas. We could still see them deciphering the sword together, only their semi on the same team now. Maybe Caroline even gets to go to the island this time and be more involved in the story line as well. The two of them discussing the fact that she doesn’t want the cure for herself under better circumstances (aka where he hasn’t just bit her). Maybe when working together the lines begin to blur more, things are less black and white, and Stefan’s own blurry morals and complicated relationship with Klaus don't help things.
I don't know that any of this actually works with how they set things up for The Originals. But honestly, I don't think they set up a lot of things for the spin-off super well despite apparently knowing about it before they started writing the season. And for all the anti-magical baby plot people, perhaps this could fix that.
I don't know if this would actually work, but these are my thoughts when I’m trying to sleep. I watched season four clips recently.
