Car was serviced and a few days later, part of the bottom pan broke off "very cleanly". Looks like it was cut. My brother, a mechanic, says it probably was to allow easier access for oil changes. Toyota repaired it for no cost very quickly. We are concerned that debris will damage the engine as the part is no longer whole but in pieces.
bottom pan broken on 2010 Toyota Prius
If it were just a plastic shield that was cut to get access to the oil filter it can not get into the actual engine in any way. If it was the oil pan that got damaged it could only happen though impact and the dealer wouldn't have replaced it free. Sounds like nothing to worry about.