Its a shame they did not. Oil fields can be rebuilt.
Actually, from what I understand, many of the Iraqi oilfields are fairly low pressure affairs - IIRC, there was some concern before the war that if many of the wells had been set afire, there was at least a reasonable possibility that they wouldn't be able to reconstruct them. Perhaps PW or someone else with more understanding of oil geology can comment on this, but I do strongly remember hearing something along these lines. If that's the case, it may have been a bit harder of a choice than it might appear at first blush. Sacrifice priceless historical treasures, or sacrifice the future wealth of the country....
In any case, it's done now, so probably the best thing to do is to make an offer of general amnesty for returned artifacts as soon as it's feasible, or perhaps even seek money to start a reward fund for returned artifacts.