I fixed your post (That is, if we want to act like mouth breather Steelers fans).
Beyond being a bush league move, it was a truly stupid act by Tomlin, whether it was intentional or accidental.
If his positioning was accidental, I think you have to question allowing him to make any critical decisions. He didn't realize he had walked that far away from the bench area and had one foot on the field? And he chose to watch the play on the video board without being aware of what was happening around him? This would be like a highway crew foreman almost getting run over by a piece of equipment because he decided to stand with one foot on the road instead of actually watching the equipment from a safe distance.
If his actions were intentional, then you have to wonder why he thought this would be a good idea and if he believed he would get away with it. On one hand, it did prevent a touchdown. On the other, he had to resort to the kind of tactic an 8 year old would think up. As many questions about Tomlin's judgement the "it was an accident" explanation raises, they actually worse if he did it on purpose.
As far as the topic of whether the Steelers will keep Tomlin or not, it all depends on if they think they can win with him. A few years ago, James Harrison and a lesser known wide receiver were both involved in domestic violence situations. The lesser known player was quickly shown the door. Harrison stayed and the team owner even offered a misguided defense of his actions. If Pittsburgh moves on from Tomlin, it will be based more on the fact that the team hasn't won a playoff game since 2010 than this incident.