If he has the waterpump w/ the plastic impeller, then it could've very well failed. Happened to me . Check the oil for antifreeze, if there is none then do what is mentioned above. If there is...
To answer your other question, a V6 swap would be too much work. The good news is that it shouldn't be too hard to find another Zetec if it comes to that

Contour--It will make a master mechanic out of you! 95 LX MTX Bolt-ons 95 Neon SOHC ATX 77 Dodge Powerwagon-more displacement than my Neon, Contour, and wife's Saturn---combined!