Thanks for sharing your Quark story Wesley. For some reason, I found myself chuckling just picturing you asking people "Have you seen my Quark?" repeatedly. I'm guessing you never found it?
I totally get where you're coming from on the topic of resentment. Long-term harboring of negative emotions takes a toll on you, while the other person probably just carries on with their life. Your negative feelings just weigh you down and eventually, you have to let go. Not because you've necessarily forgiven them, but because the toll of the emotions is no longer worth it.
On the other hand, I feel very much glued to anti-wrongdoing. Of course, at the end of the day, Quark or no Quark, life keeps churning, like you said. However, I'd feel very much disturbed about the wrongful theft of something that belonged to me. I probably would've gone Sherlock Holmes too.
Giving a shit about something of yours being stolen from you doesn't make you a petulant child who lost their toy. Letting wrongdoings slide simply because they derail you from the big picture isn't always the answer. This isn't to say that you should start a witch hunt, but I argue that consistently letting things like this slide creates repeat offenders. As if one act of theft wasn't enough.
I'd get over it eventually, but I'd still have my radar on, ready to catch the thief if and when they reveal themselves.