I think if the IOC ever seriously thought there was a good chance something might happen to the athletes somewhere, they'd probably break out the heavy-arm tactics. I don't know if they have any protocols in place, but when Russia's effectively violating Olympic principles threatening gay athletes, I'm sure they can call them on that or at least threaten to.
In this case, though, I think they've figured Putin simply will not allow the kind of backlash that would come from going after one of the athletes.
Which is a pity, because I think the only thing that would really work is if they figured out a way to declare Russia had forfeited the right to host and then to move the games(the former should now be easy if they ever really want to do it, but the latter of course...). Way too many of these Russian politicians would probably love if the US didn't come; more medals for their athletes. Putin would know better, but I can't help but think he's smart enough to ultimately turn a boycott to his own advantage.