CLIMATE CONTROLS NOT WORKING - no heat (2013 ford fusion) - plus more stuff wrong (all at the same time)

Week and a half ago, Check Engine warning light came on, next day Engine over temperature warning light came on.  Towed car to mechanic where they found mice had eaten through wires and fixed problem.  4 days later, blind spot and cross traffic system fault warnings came on and the park assist, parking brake, and passenger side windows don't work (which I could live with) but  climate controls aren't working (nav, entertainment, and phone on the panel are all fine and functional).  As it's winter and I need defrost etc... I took back to mechanic for investigation.  I'm told that the diagnostics test showed lots of 'codes' misfiring and so they began to search for the problem.  At the time, I asked if it could still be a 'mice issue' ? perhaps they set up house in the dash behind the control panel and did damage and I was told 'probably not'.  Okay, so 4 hours later and I'm informed that they have 'more than likely' ruled out that it is anything under the hood (engine block issue, fuses, wires, etc..) and the next steps are to start removing the dash from inside the cabin.  So after 4 hours and not knowing what the problem is I left because (a) they had only allotted that time for the problem to be fixed and (b) I need to think about money and if I can afford them to 'explore' for the problem when it could take an uncertain amount of hours to rip out the dash.  So I have to wonder after this experience, do onboard computers not help mechanics pinpoint problems?  Possibly not exactly what the issue is but the general area and components of the car that are malfunctioning?  Has anyone encountered this issue before I spend another sizeable chunk of money on investigating to find the problem and then repair ir?  I realize part of finding the problem is to explore but can't this be narrowed down instead of figuring out the problem by way of elimination?  Thanks.