there's wiggle room - b/c he may have talked to the ambassador in his role as a Senator and not as an agent of the Trump campaign. that may be enough for him to wiggle out of this. maybe.
still...there's enough here to merit an independent investigation since Sessions is the AG and it would be improper for him or his agency to head up any investigation into this Russia shit since he MIGHT be implicated.
so while this situation may not result in Sessions losing his job it SHOULD be enough to fuel the push for an independent investigation where previously there was much hemming and hawing about that.