It also depends upon the nature of the emergency. A 4-engine a/c with one shut down as a precaution is one type of emergency. A 2-engine a/c with, say, an uncontained compressor failure which might then have caused airframe damage and / or fire is also an emergency. Very different types though.
My considerations would be: is the emergency able to go-around and divert in case the runway gets blocked ahead of it? If not, I'd sterilise the runway as soon as possible.