Helm is alive during the events of the campaign
Page 294 of the Player's Handbook lists Helm in the deity pantheon for the Forgotten Realms. Based purely from this, I think it's fair to assume that Helm, along with the other dead deities who are listed on the pantheon, are resurrected as far as any of the 5e published adventures are concerned.
Additionally, Ed Greenwood and Robert B. Marks did an AMA on reddit a while ago, where Greenwood confirmed that Helm has been resurrected, but the exact mechanism, at least at the time of the AMA, hadn't been fleshed out yet. Specifically, he said:
Helm: Yes. The story? Don't know. Yet.
I do not really keep up with the published storyline of the Forgotten Realms, but based only on some quick research it would appear that The Sentinel by Troy Denning includes a Chosen of Helm as one of the main characters. The book takes place in the year 1486.
With all of this combined, it's pretty much certain as far as I can tell that Helm was indeed resurrected during the events of the Second Sundering and would still be around in 1489 for the events in Hoard of the Dragon Queen.