  {deletions}
Yes, this is a valid concern IMHO.  With the directly attached fan units I've
seen, it looks like if the fan were to stop the chip cooling would be 
a good bit worse than no heat sink at all.  In other words, if the fan stops
the unit turns into an insulator and the chip might get hot enough to
suffer permanent damage, not just stop working temporarily.

My Zeos 486DX2/66 (tower case) has a passive heat sink on the cpu, and it's
located so the front fan, which sucks air into the case, blows right on the
heat sink.  If that fan stops the heat sink is still cooled by convection air
flow so should not see too dramatic a temperature rise.  Essentially the 
arrangement you're talking about and a good idea IMHO.
