There are 2 kinds of data stored on AWS, the form itself and the attachments related to each submission. The data of the form is saved into the Database (DB) and the attachments are saved into Simple Storage Service (S3). The stored data in the DB is never deleted unless you delete the data yourself. The collected data on S3 is also never deleted, unless you delete it yourself or you end up using more space then you're allowed according to the OCHA/HHI policies.
You can keep up to 10 data exports at a time per project. If you create an 11th export, the oldest one is deleted and only the 10 most recent exports are kept.
For more information on KoBo data security measures, please refer to this other help article.