A few points:
The 300-pound, 25-year old player (Tyrunn Walker) that crashed into him later broke his own leg. He's out for the season at age 25.
"Fred isn't going to come back as fast at this age": Hard to debate, this is pretty much the way it is. Anyone who thinks differently, is probably not yet 30 themselves. Slow recovery from injury is probably a bigger problem than extra chance of injury at age 34.
Fred got injured on a play that would probably have injured a much younger player as well, in my opinion.
"Fred has a high ankle sprain": I haven't seen anything that definitely states this. If he does get the "dreaded" high ankle sprain (I'm not sure how someone said "high ankle sprain" without the word "dreaded") then they might send him to IR, unfortunately. Link?
"Fred is injured now, so he wouldn't have helped us if he were on the Bills": No way to know how a hypothetical scenario would play out.