Executive orders cannot supersede or go against the law. The courts would quite rightly shut him down.
Yes, but the president is the head of the executive branch, which includes the DoJ. He can simply instruct them not to prosecute.
That does leave companies like Oracle, who TikTok uses to host their content, in a weird position where they could be fined by future administrations for continuing to provide them service now.
However, the law does give the president the ability to give them a one-time 90 day stay of execution. So, theoretically, they could repeal the law in the next 3 months.