There are big differences between the 2014/15 Hearts and what next season's Hearts will be. Hearts essentially knew they were getting relegated from the beginning of the season, and so spent a lot of their time preparing for the following campaign. This season Hearts just kept digging themselves into a whole desperately trying to avoid it, with little plan for the future, and it's backfired. Ann Budge and her consortium were just coming in then with their resources, allowing for easy funding for a really good side. While Hearts likely won't be short of that despite the fortune they spent this season, Budge is heading oot and the club will be fan-owned, which I personally don't think will work out at all for them. They've already admitted that any Championship push would have to make large use of their (admittedly deep) youth system, and I don't see the kind of planning or ability to invest in a side that created the efficient 2014/15 side.
Tl;dr - I think they could potentially shit the bed and am looking forward to see how.