How could it not help if Henning was that bad, call some of your own plays. What strengths in other areas? Nolan was doing a fine job running the defense ( most of the season), Hennings offensive plays were bad or didn't fit our personnel and he did fire the special teams coach because he was so bad. I understand you might have to run with Henning til the end as a titular OC but I would have replaced his play calling. You cannot just do nothing with the offense falling apart all around you.
Edit- My point being the head coach is the "boss" on the field, he oversees the company and needs to make it run smoothly given the quality of the employees you have. In the end the credit and the blame often are placed solely on the bosses shoulders.
To Tony's credit, he did make reasonable decisions. Knowing he couldn't fire his OC going into December with playoff aspirations, and knowing that he can't change the mindset of a 67 year old OC who has been running the same offense for past 40 years, here's a reminder of what happened:
1) He tried putting Pennington into Henning's offense. If he hadn't got injured we would have won more games and we probably wouldn't be having this discussion.
2) Henning liked Thigpen way too much and didn't run the ball at all against the bears, causing us to lose
3) Henne executed a beautiful, nearly perfect game in Oakland. This misleads everyone into thinking execution has been the problem.
4) Henne played like absolute garbage from that point on (mainly in terms of turning the ball over, which he thinks all of a sudden "isn't life or death"), the offensive line went to hell, and we faced some pretty good pass defenses (Browns, Jets, Bills).
At this point the only thing I can really fault Tony on is that his OL fell apart and that is entirely on him. Other than that the worse thing I can say about him is that he's not a mastermind who's going to pull through against all odds in these circumstances, and he mis-manages game time now and then.
Just personally/subjectively, Sparano isn't my kind of coach in the first place. He's a parcellian, leaning on the defense and the run and playing not to lose. I've always wanted a west coast gunslinger coach in Miami, especially with how pass-friendly the league has become, but to be objective, historically both philosophies have been and probably can still be successful.
But honestly I don't think its the end of the world if he stays. I don't think he's holding us back from being a superbowl contender. We just need a mastermind OC and some weapons.