Grunching for fun:
1) If you're meeting with a loan shark to pay back a loan, and you need to be there on time or he's going to shoot your dog or worse, you should probably go. But you'd have a better chance of getting there scud-running VFR for 300 miles than trying to fly in icing. If you can't scud run due to terrain, maybe you can make a home-depot run and rig up your own de-ice system. Get some drip-lines, duct tape and some glycol, rig up a venturi on the end to create a vacuum. How much do you care about your dog?
2) Tell ATC and turn around. It's difficult to fly IFR without the HI and AI, and illegal anyway. Also, you'll probably die if your electrics fail, and if you're having a bad enough day it probably will. If you're still worried about your dog though, make up an excuse and see if ATC can get you an altitude out of IMC. If they can't, now is the time to read the manual for your autopilot and find out if it's coupled to your turn coordinator. Set it in NAV mode or whatever and have it follow the GPS or VOR (disclaimer: I don't know how they work, I haven't had an emergency and therefore have never had to read the manual).
3) Recycle the alternator. If that doesn't work do it again. After that tell ATC. Remember that all those dials that tell you how to get to the airport are powered by electricity.
4) Go missed
5) In poker we have a saying:
"Hey limitedslip, I got this problem. So I was at home screwing the cat, and my wife walks in, catching me red-handed, vaseline in one hand, cat in the other. Just disgusting. Now she wants a divorce, and she wants all my money, and the kids. And not only that, she called the cops on me, so I'm probably going to prison for animal cruelty. And I don't know how they treat animal abusers in prison but it can't be good. So what should I do? What would you do?"
"Well, I wouldn't have screwed the cat."
The lesson here, is DON'T SCREW THE CAT. Don't accept a hold without an Expect Further Clearance time, don't sit there and let your fuel run out and then wonder what to do when you're out of fuel.
6) You didn't specify whether you responded to the altitude change request. I'll assume you did, and that you subsequently realized that it would take you into a mountain. You can a) ignore the request and descend once clear of the terrain. The downside here is that your AOPA lawyer might have to explain to the FAA why you didn't descend into a mountain, killing all aboard or b) fly into a mountain, killing all aboard.
Looking forward to more questions.