Emo dumps Carver, the Carver site is down.

I wonder who will handle existing 7 yr-warranty on my VTA180 -
Bobcarver.com is no longer existed

Maybe here? http://www.carveraudiorepair.com/

This site is 3rd party who handle Sunfire Corp. solid state products.
I don't think it handle Carver Tube Amp - and who will pay for the repair bill?

- and who will pay for the repair bill?

Unless Emotiva markets the specific line, I would not necessarily expect them to handle warranty issues. This seems to be a little different relationship than say, when Conrad Johnson purchased McCormack because they immediately continued to carry and sell the line, and they took over warranty service, I believe. You should contact them and ask.
Aren't tubed amps relatively easy to diagnose and fix, unless you fry something irreplacable like the transformers Bob wound special? There are several noted repair folks around the country who should be able to help if you ever need it.

At the end of the day, the acquisition really isn't the relevant issue here.

Barring some clever deal structure (unlikely to be effective, I'd think), when Emotiva acquired Carver, LLC, I'd assume that they inherited Carver LLC's' liabilities attendant to warranty service. They would be on the hook, unless/until they bankrupted Carver, LLC (very likely). In that case, it's up to the courts to determine how much Emotiva is on the hook for warranty claims. I'm sure the banruptcy court will try to protect consumers, to the extent possible.

But, don't blame Emotiva. Presumably, Bob Carver cashed out on the sale. Even if he hadn't sold, he might have bankrupted the company, too. You'd be in the same boat.

Whenever you buy from a small company with limited financial resources, you run the risk of bankruptcy - whether via the then owner, or any future owner.