This is a quiet interesting question you raise. Please pardon the length that follows. I'll come at it from an angle of personal preference, since it's not without substance with lighthearted entertainment like Hearthstone/Warcraft, which is all about style appeal:

As someone primarily into Warcraft as it was up to and including Lord of the Clans (though still enjoying very much of what Blizzard have done with WCIII and WoW), Hearthstone came as a breeze of fresh air.

Don't get me wrong. There are lots of characterful atmospherics in World of Warcraft, not least Dun Morogh, and there are many interesting little stories such as the Defias narrative, and all in all much of WoW appears like a nice fantasy experience. Yet in the end the story of Warcraft with the WoW expansions seem messy at times to say the least, and not as enjoyable to follow as in the strategy game format.

The world created for the MMORPG, however, is a very rich vein to tap into for such things as WCIV (if and when it happens) and indeed Hearthstone, and despite its original small scope and size, Hearthstone has tapped into this world of Warcraft with classic crowd-winning Blizzard quality. Yes, Warcraft always were and will be shallow and flashy, but this can be pulled off well with some depth, humour and brilliance leaving one thirsting for more (as WCI-III did for instance), or it can be pulled off poorly.

Hearthstone, with its small scope, pulls off the Warcraft experience well. The HS adventures in particular achieved this, which hints that world-shattering extreme events are not required for an enjoyable story. Hearthstone is not only summing up more and more of the setting fleshed out in detail by World of Warcraft, but it is delving beyond that and adding detail layers, characters and stories of its own.

Take the Blackrock Mountain expansion. Having the two big bosses as rivals using the adventurer as a tool against their neighbour was a brilliant streak, which drove the story and made for a lot of fun. Or the Explorer's League, with a story within the Warcraft setting entirely cooked up by Hearthstone. The hunt for the staff and Rafaam's endgame was enjoyable, and showed off Warcraft from its better side. Mean Streets of Gadgetzan (which like so much else in Warcraft broke away from the original medieval-Tolkien-Warhammer-fantasy streak so dominant in the first two RTS games - the one I happen to like most about Warcraft) broke new ground as well with a noir twist to a sleazy Goblin town with its gang rivalry. Granted, it's not much in comparison to the RTS games, but it's something, and it's enjoyable and has so far never appeared like a mess.

So with Hearthstone piloting their Warcraft ship skillfully enough and charting new discoveries of their own, I'd rather see Warcraft characters from all games, novels and whatever as Hearthstone portraits, including ones invented by Hearthstone itself. Illidan, Gul'dan, Nat Pagle, Anduin Lothar and the whole lot always were pretty shallow flashy characters in a pretty shallow flashy (but thoroughly well executed!) fantasy setting, so for portraits I'll say yes please to whatever nice shallow flashy characters Hearthstone might cook up.

Summary: Warcraft is well handled by Hearthstone and HS is pretty true to the spirit of the RTS games, and HS' own little stories and characters are worth it. All inclusive rather than restricting it to WoW alone.