No. Cancelling your Iridium GO! or Iridium GO exec airtime plan does not cancel your PredictWind Forecast subscription.
These are two separate services:
Your Iridium airtime plan provides satellite connectivity for your Iridium GO! or GO exec and is managed through the PredictWind Satellite Portal.
Your PredictWind Forecast subscription provides access to PredictWind weather and routing features and is managed separately through your PredictWind account.
If you no longer require either service, you need to cancel each one separately.
Cancelling your Iridium airtime plan will not stop your PredictWind Forecast subscription from renewing, and cancelling your PredictWind Forecast subscription will not cancel your Iridium airtime plan.
Before cancelling, check which services you currently have active and make sure you cancel each one you no longer require.