Yes, Heroes of the Storm is still around.
Although I wish the development team had more resources and backing from Blizzard, the team that does remain is doing a fantastic job of keeping everything fresh, delivering new events, mechanical shakeups and hero reworks alongside of a balance patch cadence. I'm still playing it weekly: I never stopped.
And this is a great time to get back into the game actually, because a new PTR patch is completely changing many facets of Heroes, mostly for the better: on paper at least. One of the biggest alterations is the way the core (the final objective you need to destroy in pretty much any MOBA) now works. In short, each individual map will now have a different core ability, all of which line up thematically with the map in question.
So Blackheart's Bay, a pirate-themed map, will launch cannonballs at you. Garden of Terror, a plant-based zone, will polymorph you into little plants (a nice callback to the way the map used to work). That sort of thing. Over Bro Media has a great rundown of the concept below, where they show off every new interaction. Alterac Pass is omitted as it already has a unique core, as is Towers of Doom, as you never directly attack the core.
Now all of this is part of a "Nexus Anomaly," an experiment-based change that could be removed if the community doesn't take to it. But for now, it's one of the most Heroes-feeling things in recent memory, and I'm including the period when it was fully supported.
You can find a full list of all of the new core abilities below, to match up with the video. As a reminder, all heroes are free-to-play until April 13.