Chang's departure from HTC is likely due to the company's steadily decreasing smartphone sales and the fact that it was unable to regain its footing in its home country of China. Further, the reason for the resignation is mentioned as a "personal career plan". Chang previously used to work at Motorola and Goldman Sachs before joining HTC as CFO in 2012.
Despite selling off most of its smartphone business to Google, HTC is not leaving the smartphone scene.
As for the smartphone market of HTC, it has not completely ended its business.
Although the company is facing troubles for quite a while, yet it seems like the company will be launching its promised flagship of 2018, apparently HTC U12, in coming months. The company has announced that it's Smartphone and Connected Devices Business president has left the company. Some speculate that the HTC U12 might be the company's last flagship, but nothing is confirmed at this point.
It's been a rough few years for HTC. The company lost significant ground to rivals in recent years, however, and despite its efforts to catch up and get back on top, it's still struggling to return to its glory days.