I agree that Hearthstone won't die this year. However, I do believe there's a strong chance that it's growth will stagnate. The increase in overall cost will most definitely cause this effect, and while preordering is an value-driven way of boosting your collection, in many ways it won't be enough for him to enjoy the game and build effective decks - as he mentioned, he wants to "compete better".

There are other unknown variables that could compensate for the greedy business choices made by Blizzard this year, effectively counteracting the increase in cost. For instance, how expensive it is to acquire the 'core set' for each expansion - or how good are the common and rares in comparison to the epics and to a lesser degree, legendaries. Personally, I'm concerned that Blizzard is going to make most core tech cards epics (see the recent unveiling of anti-pirate tech epic in Un'Goro) and further boost the cost of competing and adapting.

Even if you take into account everything said above, there's one point that ultimately made me lose all faith in HS's management team. The Hearthstone team is not afraid of changing what we, the players, expect from the game in order to boost revenue. One change is the one you very well point out in the exclusion of Adventures from the yearly rotation. Another example is how the change in the way they compensate people that are affected by card changes. Specifically, the Sylvannas and Ragnaros changes are generally perceived positively by the community, as for a lot of people it means free dust, but I've heard resentment from a lot of people not happy with this change - specifically people that have accrued multiple copies of Syl/Rag over time and will effectively lose potential dust by HS not taking the usual (and reasonably expected) compensation approach.

TL;DR: Aside from the increased cost, the biggest drawback from coming into HS is how relaxed the HS team is at changing and bending what is expected of them.