If I delete my OpenID account (not only way to log in, I use gmail), will I lose my stackoverflow account with it? (or any account i use with it)
Will it also remove the points I gained on other accounts for having the account?
If it is the only way for you to log into Stack Exchange sites, you may be out of luck.
But, as you stated that it isn't, deleting the openId account itself, and removing it from the list of logins (in your profile page, Settings tab, My Logins section) wouldn't do anything else to the account. You will be able to use it and log in with any other openId provider you have chosen to use.