I would say for your average leisure/amateur rider that's beyond their capability and I would say its far far better to PTS than pass the horse on to an uncertain future. I have to say that personally I would never fully trust or feel confident about a rearer, even a reformed one (talking about a true 'full on' habit of standing up on 2 legs while ridden, not a playful youngster that's gone up in hand, or a nappy sod that bunny hops up in a strop, very different things IMO), perhaps this is just an unfair perception but I would say it's the most dangerous of all the behavioural habits (particularly if unpredictable) and I could never be confident they wouldn't revert to type if anything ever hurt or upset them even if the original problem was fully fixed. With the best will and most careful management in the world all horses have occasion niggles or frights and they need to be able to reliably cope.
I agree with all of this. I used to work with someone who had grown up working at a dealing yard. Dealers she worked for used to take on and 'cure' all sorts. Some of the methods they used then would now be considered quite brutal it's true. The one behaviour they were all very wary of was rearing. Anything else she said they would take on and cure the horse but not that. Much of it was because of the danger level. You don't just risk falling off - it's having the horse land on top of you.
The other problem is that most riders, all but the most experienced professionals, will reinforce rearing and inadvertently train a horse to rear. If a horse goes up you'll almost certainly release the pressure - whether it's leg, or rein, or asking a horse to deal with something it doesn't like, you'll stop doing it. So the horse learns it's a great way to get out of a situation. So much as I would like to give every horse a chance and thoroughly check everything to give them the best chance, I am very wary of rearers. PTS may be the best answer, in the interest of human safety.
That said, my first horse reared but in all honesty it was a very balanced levade. It felt much more like he was just playing. It was never threatening or felt remotely like he was going to go over backwards, so it does depend on the circumstances.