Someone already said this, but I'd like to co-sign... that's not 42 hits, it's 42 pressures. And pressures is a somewhat subjective metric. I haven't charted it, but I think 42 is a bit high.
Other things to consider: Did you know that, before Sunday, the Colts hadn't run a single offensive play with the lead? They've been playing from behind a lot, which means more obvious passing situations (almost the entire second half of the opener, for instance), which means more aggressive pass rush.
Also, Luck takes more time to throw than almost every QB in the league, and his average depth of target is deeper than any QB in the league. If QB1 is generally quicker to throw and attempts shorter passes than QB2, you can probably count on QB1 facing a lower rate of pressure than QB2.
This is why, especially with offensive line play, there's no adequate substitute for actually watching the games. Even better is watching other teams play, so you can get good context. The Colts protection hasn't been great, but it's definitely improved. Reitz has been leaky at RT, whether it's due to injury or him just not having it, but he either needs to sit out or get it together, because he's the weak link right now. AC has had troubles, too, but he was better Sunday, and will be fine. There are injury issues at RG, but between Good and Haeg, assuming they get and stay healthy, I think RG will be okay. (I definitely don't want to see anymore snaps of Blythe at RG...)
The post was in response to the OP, who basically asked 'what's the worst that could happen?' Yeah, there's lots that can happen, which is the answer whenever someone questions a conservative decision.
The real question is about risk/reward, which is how basically any binary decision should be graded. The risk is something catastrophic happening, and the chances of that were considerable, given the fact that the protection was leaky all day, Luck had given up a sack/fumble/TD at the end of the first half, and he'd thrown a pick earlier in the second quarter. Lots could go wrong.
The reward would be a first down, or even a TD. But on that drive, the offense was a mess, the calls were going against the Colts, and you could assume that any well coached team would be very passive in coverage to avoid a cheap defensive holding penalty for a five yard automatic first down. You never know, but you're playing the odds, and the odds weren't in the Colts favor on that drive.
Besides all that, it's early in the 4th quarter, you have a tight game, you're at home, the defense is actually playing pretty well, especially in the red zone, and your offense has been moving the ball effectively when they avoid big mistakes. The smart play is to flip the field, rely on your defense, and let the offense get the ball back with a chance to deliver the lead. And that was the eventual outcome.
The sequence almost worked out for the Colts, by the way. The Chargers muffed the punt and the Colts almost recovered.
I know fans always want to see the team go 'pedal to the metal,' but the Colts did the smart thing there. (Fans in LOS were even booing when the Colts kneeled it out at the end of the first half, which is a ridiculous response, IMO.)