I must away and tend to my ravens
The decision to have Orton challenge Sheamus definitely indicates that the decision had been made to allow Orton to turn face. Had they not made that decision I suspect the Kofi feud would've gone differently. I suspect Kofi would've won at TLC and the feud would've continued into The Rumble. One scenario I could see working is for the 2 of them to really go at it in The Rumble match and, just as Orton is about to eliminate him (one of the slow ones where they try to force their opponant out) Ted sneaks up from behind and takes them both out. That would allow Kofi to retain a huge amonut of momentum while giving Orton a reason to move on to The Legacy feud. Orton's inevitable punishment of Ted for his betrayal would've, in theory, given Dibiase the crowd support he needed going into Wrestlemania.I could've sworn Randy Orton practically tried to maim Kofi earlier in that evening by throwing him off the stage--merely for making it a one-on-one contest in the Iron Man Match between Orton and Cena the previous night after Kofi chased DiBiase and Rhodes away with a chair (which followed Cody blaming Kofi backstage for losing to Team Smackdown because Big Show happened to Chokeslam Kofi when Big Show turned on Team Raw).
Orton was definitely the heel in that feud. It was his last feud as a heel.
As far as whether or not the Orton face turn was an accident or not, I think we have to remember the dirtsheet reports circulating in early January. The writers knew they wanted to have the Legacy blowoff to happen at Wrestlemania, which had been obvious for months beforehand. But there was strong disagreement whether to go ahead with Plan A and have DiBiase be turned face against Orton (and probably Rhodes), or go with Plan B due to the fans clearly cheering for Orton much of the time in the previous year anyway despite being a heel, and turn Orton face. There was an argument that raged for a week or so within WWE creative, with many people split on the issue.
Well, judging by the very next few weeks, they made their choice and it was to turn Orton face. Everything--from having Orton have a mini-feud with fellow heel Sheamus, to Legacy blundering in costing Orton the match against Sheamus at the Royal Rumble, to DiBiase turning on Orton at Elimination Chamber, to DiBiase and Rhodes scheming to turn on Orton only for Orton to be aware of the plan and attack them instead during the Raw the night after Elimination Chamber to the Legacy duo beating Orton up while Sheamus beat up Triple H, therefore equating face Triple H and newly-turned Orton with one another against "the young guns" as Michael Cole called them, i.e. hungry heels--from January 11 through Wrestlemania was designed to turn Orton face. It perhaps started as an accident as an idea, due to the fans going with Orton, but the turn itself was meticulously crafted and planned sometime in early winter.