Hey @Phoebek, thanks for reaching out! I completely understand your concern about keeping your files safe.
Rest assured, your work will not be deleted when your Education plan expires but you will not be able to edit any files on your education team. If you have more than 1 project, 3 files of Figma Design and FigJam each, they will be locked out (cannot be edited) until you resubscribe. After expiration, you can upgrade your team or transfer 3 files to a free team to continue working on them.
To help with accessing your files once the education plan expires, you can upgrade your team to the Professional plan if you want to keep all your files and projects as they are: Upgrade to a paid plan
Alternatively, you can reduce the number of files so that it fits within the limit of the free Starter plan which is 1 project, 3 files of design and figJam each. I recommend to move additional files to your Drafts section, or create other teams and move the files there.
Here are some helpful articles for your reference.
Also, please take a look at the updates to Figma's pricing, seats, and billing experience: https://help.figma.com/hc/en-us/articles/27468498501527-Updates-to-Figma-s-pricing-seats-and-billing-experience.
I hope this provides some clarification. Please let me know if there is anything else I can assist you with, and I will do my best to help.