The issue is not the 757 per se, but the particular Pratt & Whitney engines that are used on this model. I'm sure the 757 comes with more than one engine option

The issue is not the 757 per se, but the particular Pratt & Whitney engines that are used on this model. I'm sure the 757 comes with more than one engine option, and more than one model uses the particular P&W engines (although this one is less likely). In the worst case, the 757 fleet that relies on this particular engine may end up grounded while the problems are worked out while the rest of the fleet continues operating as usual. This is not entirely a novel situation; there have been plenty of occasions where problems with a particular engine model have been addressed with not much harm to the operator, and the plane manufacturer. I don't see how this affects Boeing big time, when you also combine this current situation with the fact that most 757s are already set to be put out to pasture in the next 5-6 years.