Yes. Your reports regarding a campaign you have sent out are and will always be available for you to view. You can view the default campaign reports or visit the Performance Overview page.
The general statistics of these reporting options, for example, the total/unique percentages (Open rate, Click through rate, etc.) and the total/unique reporting numbers, will still be available; however, you won't be able to see or export emails, as those will be archived 6 months after your campaign has been sent out. Also, note that emails that have received your campaign but have not interacted with it, are only listed in your report for 90 days.
This is adequate time for you to export your recipient-based statistics as a CSV or a pdf file should you wish to retain this information on your past campaigns.