Hi Tiana,
Budgets should be considered as separate entities from Campaigns. Although a budget is associated with just one campaign, if it is a shared budget, it can be applied to other campaigns later in the future. Even if it is not a shared budget, if the campaign associated with the budget is removed, then that budget is orphaned and can be reused or deleted as needed. Automatic deletion is not supported as the decision is left to the user to reuse or delete budgets as required.
Regards,
Shwetha
AdWords API Team.