I agree with Keith that the market is not falling apart on SxS. It has and will be a niche market. Those of us in our 50's to 80's are still collecting and others will follow.
I do believe that prices on field grade guns are not growing, but that represents bargains to be had. Also that some niches like Belgian and French guns are under valued and may likely stay so. Again that offers a good entry value. SxS guns have not been dominant in the market for decades for a number of reasons to include relative cost. They will continue to be a niche market, but as such they will not disappear of totally lose value
Small bores are holding and growing value faster than 12ga, but that should be expected. I doubt I will be buying many heavier guns to hunt with as I grow older.
If people are buying to speculate on future value growth; my advice is to buy good mutual funds. Most of the time guns will not return better than the market, unless you brought it a great low price to begin with (rare to almost never for me).
My fear for our future is that hunter numbers are declining and I always have a little sadness when I see a great old gun in mint condition because while beautiful it represents a potential for great use unrealized, at least yet. The guns I love are made to be used and have their value to me in their proper use.