extra 6 months of exclusivity and ST Microelectronics will be allowed to sell the part in question to only Nokia during that period of exclusivity. In addition ST Microelectronics will also have to face a 10 month ban during which the company will not be allowed to sell the part at all.
So the bottom line is that HTC won't have to replace the HTC One units already made. The only problem is that they will have to find a replacement source for the part in a hurry. HTC might end up paying more for the component from another vendor, which could eat into margins a bit. But considering what the worse case scenario could have been, things worked out okay for the Taiwan based company.
source: AllAboutPhones (translated) via AndroidCentral