Irreplaceable individuals don't exist. Some are just harder to replace than others.
I don't think Moyes even comes into that bracket. Given the facts:
Buckles under pressure in most big occasions.
Reverts to type - Nev in Midfield, Cahill attacking mid even though it hadn't worked for 2 seasons. (West Brom most recent example) regardless of form. This one is also applicable for formations.
Poor at making substitutions (Coming off Louis Saha to be replaced by Sylvain Distin...) Don't believe any other prem manager would've done that.
Sure, he has great qualities too, but I'd rather see someone else given a go, and can never wrap my head around the attitude that without Moyes we'll get relegated. Essentially no, lets not pander to accommodate Moyes.