A few thoughts:

1. Is the tent a goner? I can't imagine how I could fix the integrity of the fabric itself, but I thought I'd ask anyway.

I think it is a goner. And I am not sure it is only because of the bug spray. I have an old North Face tent that has been stored properly, but it still suffers from this kind of deterioration. No idea how to fix it.

2. What are the "good" technical manufacturers these days? Has Mountain Hardware gone the way of North Face?

There are quite a few good manufacturers...but how and where do you use your tent? That would make a difference. Big Agnes, Marmot, MSR, and even REI make pretty good equipment, as do others.

3 What tents should I be looking at to get similar features to what I had with this one? I'm ok with a slightly heavier backpacking tent to get the features I want. If I'm really going lightweight, I just take my Hennessy.

Or a tarp? We use a Henry Shires Tarptent and are very happy with it...