Perhaps the share price of BSX will drop, but not because of AVE. BSX does not have a stent approved in the US yet, so there is no "market share" to evaporate in this regard. And AVE does not sell stand alone balloons in the US. As a stretch, it does not appear that AVE stents need a "post dilatation" balloon, so BSX may lose some of that market (as will any other "high pressure" balloon makers that sell into the post-dilatation market).
GDT stent and balloon systems have seen a huge uptake in the last several months. I would imagine BSX is losing some balloon market to this situation. And Cordis' Charger has come onstream to great reviews.
Until BSX has a stent approved in the US (PMA is supposed to be submitted right around now, then add 6 months to that as an estimate, although AVE only took 140 days, and GDT even less), then it won't lose stent market share in the US.