Double up: one to play with, one to keep safe. In fact, that's what I've done with some of my favorite Masterpieces.
Regardless of whether it's a prize toy or not... get annoyed. Then try and fix it. If fix isn't possible, then time for a replacement! I've done this with several, but never actually bought a replacement!
Bemoan the fact that I'd have to track it down, purchase it, and reapply custom paint to it all over again...
into I don't think I'd get pissed off, it would be this really long period of "did that really just happen". If I didn't already have a replacement I'd go and try to track another one down. Although if we're talking my G2 Prime, I might just suck it up and live with it. No matter what you do you can't replace the memories attached to the figure.
Come on to a message board and throw a tantrum about HasBlow's horrible QC, that plastic quality sucks and that I am entitled to so much more because I'm a true fan and they need to keep me happy. Or, you know, buy another one.
Depends on the circumstances. There are a lot of questions which would factor in: Was it an accident? Was I responsible? Someone else? Adult or child? Someone I'm close with or a stranger? Irreparable or a relatively simple fix? Not to mention the questions each person can only answer for themselves with the specific item: Is a replacement readily available? Is the value more sentimental than monetary? Regardless, though I am a man-child, I'm still an adult, and will try to act as one. I won't say that I won't be upset, but I would try not to overreact. Things are things, after all.
List it on eBay as 99% mint, like when a figure is missing 1 of 4 accessories and they say it's 99% complete.
Broken out of the box , I send it back . Broken because of me ? I punch myself in the face and try to fix it . Broken because I let some foolish moron actually touch my most prized possession? I kill him , then punch myself in the face , then try to fix the problem..
You know how Fortress Maximus' tower splits in half and folds back for robot mode and snaps in place by means of 2 clips on both sides? One of those clips broke on my Grand Maximus. I don't foresee replacing that part or double dipping on an extra Grand Maximus. Fortunately, one clip is enough to hold it in place. But needless to say, I was pretty upset.
I would find out the reason why it broke, hunt it down, and kill it. Age? I would travel the world until I found time, and kill it. GPS? I would travel the world finding all the gold ever and replace all the GPS affected toys with real gold parts.
I'd be upset, and try to replace it as soon as possible, especially if it was one of my very favorites, like CW Superion or Gen. Jetfire, but ultimately, they are toys and I'll live. However I do have two Superions and two Jetfires. Just in case.