I'm not freaking out at the OP, just people trying to get this guy to screw up his engine. There is no engine in the world designed for that sort of mishap; that's patently ridiculous. I've not been too deep in one of these engines, but I've been through hundreds of others. Water cooled, air cooled, ancient, modern, American, German, Japanese, Italian, Russian, automotive, agricultural, micromechanical, you name it (I will disclose that I've never been in an aircraft engine, though I have been thoroughly through engines that are typically used in experimental aircraft). They all work the same basic way, just substitute a gasket here, a galley there, valves, angles, displacement, etc.
Car forums can be a wonderful repository of knowledge, but there are different types of car people on them:
-There are people who like to drive and have the money to have someone else do it correctly
-There are people who appreciate the machines and engineering and enjoy turning a wrench to maintain their own machines correctly
-and there are the cheap bas****s who don't know the difference between thrifty and cheap
I assumed that if the plastic piece were visible and could be somehow reached that would have been the first reaction, but I give the poster credit for some base level intelligence (he did ask the question after all). Sure, it might be OK to just leave it in there and hope it works itself out. Might. Why chance it? Sure, bearings are harder than plastic, but they're only engineered to stand up to substances as hard as oil... Sure the filter might catch it, but that assumes it's small enough to get through the pickup and to the filter in the first place... Sure it might be caught on some ledge or something in a position that doesn't block cooling and lubricating oil flow to some vital component, but it might be lodged somewhere that would prevent that 230K from being a 231K engine...
If you take on the responsibility of working on your machine, you have to live up to that responsibility or face the consequences. You can occasionally get by cutting corners like leaving a piece of plastic in some unknown place deep in your engine, just like you can occasionally screw your high school girlfriend without a condom. You might come out on the other end just fine, but do you really want to risk the consequences? Seized engine or 18 years of child support... It all boils down to how you handle the responsibilities you choose to undertake. The CORRECT answer to this problem is to locate and remove the plastic piece. The OP knows this (you all do), and that's why the question was asked. It might be easier to leave it there, but any parent worth their salt no doubt said "the easy way isn't always the best way."
OP, you took on a certain responsibility when you chose to undertake engine maintenance/repair, now you have to follow through. Either break it down to remove the plastic detritus (this is not difficult, and will be a good learning experience), pay to have someone else do it, or pray the round is in another chamber and pull the trigger.
< /rant>