If Trump really wanted Sessions gone, he would have already been gone - nothing happens unless Trump wants it to happen with his people.
Sure he could fire him, but it has risks that have to be weighed.
1 - Sessions is a former Senator and firing him would cost Trump support in a tight Senate
2 - No one Trump wants would be confirmed
3 - McConnell says won’t even have vote for a replacement
4 - Linda Graham used the Impeachment word when asked what might happen
5 - Sessions could compose new testimony to Mueller
Those are significant risks that Trump shouldn’t have to take. If Sessions were honorable he would resign in light of his rogue department’s actions and his inability to control it.