This is expected of Harima. I knew he would do something like this. Of course, I thought that if he beat Karasuma he would drag him to Tenma, but they reached a sort of mutual understanding and Harima pretty much gave Karasuma a "You should go see her, but you gotta do what you gotta do" type of response. Of course, if he can't bring Karasuma to Tenma, then the next best option is to bring Tenma to Karasuma. And surely enough, that's what he's doing. No matter how I look at it, this series is not going to end anytime soon. And something's telling me that there is something else coming up. Maybe a revelation or some event that will bring about the lengthening of the series. Possibly Harima and Tenma going to America to "search" for Karasuma as someone mentioned, but I don't know how hard it would be to search for him unless they fly all the way to the other side of the country, which, considering the two characters, is more than possible.. I personally wouldn't mind seeing that.
I'm not completely ruling out Oodou, but it would require the story to lengthen, which I think is a high possibility. If the series were to end abruptly (as in the next few months or so), then Oodou is done. The only way for Oodou to succeed at this point is to prolong the story. Well, as long as Harima is happy in the end, I'll be happy with the ending.