I doubt Surlies will ever be especially valuable for 2 reasons, they are produced and sold in great quantity, and readily available, and are not especially high quality. Don't get me wrong, they are nice, but if they closed down today, it would be a very long time before they were especially scarce, and the quality is not so great, nor designs so innovative that they couldn't be replaced by any of a number of currently made frames.
I think Panasonic is the next Bridgestone. I think they are already beginning to be recognized for their build quality, and of course they haven't been imported to the US for a while. The next one after that? Well the only way to guess that is if you could guess which company with a strong following was likely to close shop or stop importing. You'd need something with a strong niche following for that, but not strong enough. I'd say Gunnar would be a good bet if they closed shop, or IF maybe, but I don't have ay reason to believe either of those are brands going anywhere.