I don't think Harbaugh is the answer. He is not his brother.
I also don't think Jerry is going to make any quick decisions on his coaching staff.
But the question is rightfully asked, whoever coaches Dallas, is Dak part of the package? Must the new coach accept Dak as his QB? Let's say the answer is yes, then is McCarthy in the same situation? Has he been forced to accept Dak? If so, then why blame McCarthy if he has to play the cards he is dealt like any new coach would?
The situation is tricky for any new coach. If he wants to get rid of Dak, who is his replacement QB? If you say Rush or Lance, sit this one out. No new coach is going to step in and set himself up for failure like that. The problem is Dak is very serviceable as a regular season QB. McCarthy got him to 3 consecutive 12-5 seasons. Any new coach would take that simply because he doesn't want to take over a 12-5 team and finish 5-12 in his first year. And maybe his second too.
Unless the Cowboys decide to cut Dak and move on, which probably means several years of struggle, what HC would want that pile of garbage to deal with?
I think the Cowboys are stick with Dak for at least 1 more year. And if so, then they may as well stick with McCarthy too. I think the answer is the same as it was last year, build the running game so Dak is not as important to the offense. But a decision is coming fast for Jerry. He has to decide to extend Dak or move on. If the Cowboys had a top 5 draft pick maybe the decision would be easier, but they are drafting in the 20s again and it will require a bit of luck to find a franchise QB that late in the round. Even then most QBs fail in the NFL even those drafted in the 1st round.
I think the answer for this team lies with the defense. Offenses can get away with finesse and speed alone. Defenses can't. The Cowboys have to get more physical on defense. find a few pieces here and there fro the offense but focus on getting physical on the defensive front 7. Run the football and stop the run.