We can't tell if they are dying without looking at them. Sometimes worms don't have any pressing matters to attend to, so they take their time getting around. In general, if I nudge a worm, and it does not react, I question its remaining life expectancy.

Grass clippings may or may not be OK. It really depends on several factors. How fresh were they? How much did you put in the bin? Have they been treated with fertilizer, weed killer or pesticides? Did they cause the bin to heat up? Are they a smelly, goopy mess?