The Peace of Amiens lasted but a couple of years before England again went to war.

Napoleon knew, and the American statesmen knew, that the British intended to attack New Orleans upon the outbreak of hostilities, if it were in French hands.

In such event Louisiana would have soon fallen; for any French force stationed there would have found its reinforcements cut off by the English navy, and would have dwindled away until unable to offer resistance.
Louisiana's Destiny Really by the Backwoodsmen.
Nevertheless, European wars, and the schemes and fancies of European statesmen, could determine merely the conditions under which the catastrophe was to take place, but not the catastrophe itself.

The fate of Louisiana was already fixed.

It was not the diplomats who decided its destiny, but the settlers of the Western states.