A frame time spike is covered by the overshooting point: it will basically land further down the curve, which means a point converging toward the B target.
As the delta time converges to 0, the lerp coefficient is going to converge to 0 as well, meaning it won't move. Said differently, if time stops the interpolation as well. You may enter into the realm of floating point accuracy issues at some point with low values, but I'm curious of what specific scenario you have in mind here?
> So there we have it, the perfect formula, frame rate agnostic ,
... worth noting what happens on a frame time spike.