On Tuesday, Jason Mackenzie announced on his Twitter account that today was his last day at HTC. After 12 years of working at the company and going through the ranks - all the way up to the president of HTC America, and was an EVP for the past year - Mackenzie is leaving the company. He has not mentioned where he may be heading after he leaves HTC, that will likely be announced in the near future though, as is usually the case with executives leaving companies. Mackenzie doesn't appear to have anything bad to say about the company, stating that “It was a great run and I feel blessed" in his tweet. At this time, HTC has not yet announced a replacement for Mackenzie, but it won't be long before the company does name a replacement for the outgoing Mackenzie.
With Mackenzie being with HTC for 12 years, that means that he was with the company well before Android got started, back when they were primarily an ODM (basically building phones for other companies to sell as their own, something that ZTE does quite a bit in the US). HTC has risen to become the largest Android manufacturer, and in recent years it has fallen to be one of the smaller manufacturers that releases smartphones worldwide. HTC hasn't has a great past few years, having continued losing revenue and profit, replacing their CEO and now losing their top executive for the US.
HTC has been focusing more on virtual reality in the past couple of years, with the HTC Vive being a pretty popular VR headset. HTC hasn't stopped making smartphones though, and they are looking to gain some more market share with their new HTC U series. They announced the HTC U Play and HTC U Ultra earlier this month, and both are going on sale in March. HTC is also planning to release a new flagship smartphone once the Snapdragon 835 is available, which is rumored to be around the summer-time, unfortunately. So HTC isn't gone, and Mackenzie leaving doesn't mean HTC is dead in the water, they have big things in the pipeline which Android fans are excited about. And Mackenzie leaving likely won't change much of anything for customers.