What year is your 981? At a minimum, it would seem to be at least 4 years out of factory warranty.. I know of no car manufacturer that warranties trim items like a headliner beyond the factory warranty. There are a number of descriptions here for DIY, and other ones explaining how the owner removed the headliner panel, took it somewhere, had it recovered, and reinstalled it for considerably less than a dealer would charge to do it (someone has to pay for the free coffee and muffins, and free loners, etc.) The "head-unit" can be repaired (not replaced) for considerably less than $5000 (Becker in NJ does it) - or - the wiser choice - replaced with a newer aftermarket design. You may lose some functionality if you replace it with aftermarket, but you'll have access to newer maps that generally can be owner-updated.
I'm sure Porsche will miss your patronage - you should write them and tell them that. Written and mailed letters get much more attention than emails or complaints on brand-enthusiast forums. I'm not certain what your telling a bunch of enthusiasts that you won't be buying another Porsche accomplishes, except perhaps getting it off your chest. If it achieves that goal - more luck to you!
I was - as I usually do - going to ask you to introduce yourself and your car in our
New Member Introductions forum, but I suspect this might be counterproductive since it sounds as if your ownership of a Porsche is close to coming to an end. I hope whatever you replace it with serves you better. My wife has a Lexus. They don't break (actually.. they do.. but Lexus has been known to just fix things when it's in for an oil change and not charge or even tell me what they did) but they are also intensely boring to drive, to the point, it's dangerous for me to drive it, I start to fall asleep.
Personally - if I owned your car - I'd join the Porsche Club of America, and then go to a local chapter meeting and ask who the honest independent mechanics in your area are. I'm certain several will be recommended. Using independents can cut your cost of ownership in half vs the Porsche dealer. Porsche dealers exist for (1) rich people who don't think anything of a $500 oil change.. (2) to overcharge the rich people for the privilege of overpaying for a new Porsche.
At least that's how most of the "secondary" owners look at them. 981's are getting into the hands of 2nd and 3rd owners. The 2nd owners probably have a CPO warranty so they'll still visit the dealer on occasion. The 3rd owners are enthusiasts who accept that it's an old car (8-11 years old now), a formerly expensive car (even used they're still not "cheap",) and something to look at as more a great hobby/toy that you spoil by buying it goodies and accessories. And a car where they may have to get their hands greasy once in a while, to make it practical to own and be able to eat too. The 3rd owners tend to be people who are comfortable on a brand-forum like this one, sharing experiences and knowledge with other owners, they're our people so to speak.
Welcome to Planet-9, the Friendly Porsche Forum (at least for now..)
Good luck with whatever you replace it with!