No, I don't think he's still alive.
I agree with you ~ if TH did it, she'd have concocted a better alibi. It just doesn't make sense to me that this woman who is purported to have arranged a scheme to get Kyron out of the school, kill him & dispose of his body and other evidence did it SO WELL that he still hasn't been found almost a year later, no one saw her do anything & she hasn't been arrested, yet she never thought far enough ahead to plan a decent alibi for herself? Like I said, it doesn't add up.
I think it makes more sense to think that Terri was involved in illicit activity of some sort (whether or not it was illegal, I'm still not sure) and on the day Kyron disappeared, she had been busy doing things she didn't want her husband or anyone else knowing about, which is why her alibi of "driving around" was so weak. She doesn't seem to be someone who thinks through a situation before taking action ~ her sexting so soon after Kyron disappeared, for example. Most people would realize that doing that would not make 'em look very good in the public's opinion, yet Terri didn't think about it. I can't get behind the theory that she's brilliant enough to concoct a scheme to get rid of Kyron in such a way that she doesn't get caught, yet she's also so stupid that she does things & says things without considering the consequences of those actions (such as writing emails about how she didn't like Kyron ~ a criminal mastermind would know such emails would look incriminating). I don't think she's so cocky she didn't think she'd get caught. If she were a super-cocky person, I would have expected her to talk by now, yet she isn't uttering a peep (publicly, anyhow).
I guess what I think is that Terri's a shady, gross person, but I am not convinced she is the person responsible for Kyron's disappearance since she strikes me as being not-too-bright and therefore I can't imagine she'd be able to plan & execute a kidnap/murder so perfectly that 10.5 months later, she's still free & the child hasn't been found, nor has any physical evidence been located that would implicate her. Desiree & Kaine being convinced that Terri is responsible doesn't sway me. They're being told by the police that Terri did it (well... I don't know that for sure, but that's the assumption made), so they're going to believe it. Can you imagine the devastation they'd feel if they found out the police screwed up by focusing solely on Terri too early into the investigation and by doing that, they lost any hope of finding what really happened to their child? I think parents in their situation are desperate to blame SOMEONE for their pain, but it doesn't mean they're always correct. I dunno.... maybe they're 100% on-track and Terri did do it & eventually the cops will arrest Terri & a jury will convict her. That wouldn't shock me. But it also would not shock me to one day read that Kyron's remains were found in some other state and his disappearance was determined to be a crime of opportunity perpetrated by a stranger, not an elaborate plan concocted & acted out by his wicked stepmother.