The ISS also has a Crew Return emergency escape vehicle, in case there's a debris impact with the ISS. A single astronaut could be sent down in that. And SpaceX has been very capable in sending and retrieving astronauts capable so far, and they could certainly modify software to boost the ISS orbit. Russia is probably regretting that they didn't sell Elon missiles or rocket engines, forcing SpaceX to forge their own more efficient path (with extensive NASA help).

There is plenty that can be done to remedy a crisis in the ISS, all it requires is that NASA temporarily reduce their margins of safety. There is little doubt that NASA is already exploring different contingency plans.