Lets say I deleted my account, after a while I have a question that only can be answered on SO (just an example), Can I use the same email or not?
Yes, you can. For the same reasons that you could create a second account using the same email address without deleting the first account.
I'm not really sure what the motivation would be behind either. Do note that deleting your account will not remove your contributions from the site, it will only prevent them from being attributed to you.