Unfortunately, accounts cannot be recovered once deleted. The Help Center has an article on account deletion that says this explicitly, which you can see here: https://support.khanacademy.org/hc/en-us/articles/360034662972-How-do-I-delete-my-account#:~:text=Note%3A%20Deleting%20your%20account%20is%20a%20permanent%20action%20that%20will%20delete%20all%20progress%20and%20put%20a%20lock%20on%20your%20username.%20Your%20account%20cannot%20be%20restored%20once%20deleted. 

It normally asks 2nd time to conform so everyone should probably be careful when you get 2ND ALERT and you cant recover your account