Is it even possible to permanetly delete a project?
No, it isn’t possible right now.
While you cannot delete the project itself yet, but you can delete the source code in your project by overwriting the glitch git repository with an empty new commit. This is very important if you just planned to play around but ended up writing important code onto glitch and have a fear of glitch.com getting hacked and your code getting compromised and published on the internet, or if you accidentally commited a private key to glitch and wanted to completely remove it.
on glitch website project edit page open Tools/Extras/Git,Import&Export/Write
Copy_link => is e.g. https://api.glitch.com/git/YOUR-PROJECT-NAME
Copy_user_name => is YOUR-RANDOMLY-GENERATED-GIT-USERNAME e.g. 1aaa1111-1111-aaa1-aa1111111111
on glitch website project edit page open Console(terminal)
git config receive.denyCurrentBranch updateInstead
on your local computer terminal
mkdir foobar
cd foobar
git init
git commit --allow-empty --allow-empty-message -m ''
git remote add origin https://YOUR-RANDOMLY-GENERATED-GIT-USERNAME@api.glitch.com/git/YOUR-PROJECT-NAME
git push -u --force origin master
cd ..
rm -fr foobar
on glitch website project edit page open Console(terminal)
refresh