I think what you'll see is a burst of speculative buying from GW by people who immediately try to flip it over onto eBay. Followed by a crash for minis of limited interest. Eventually, the prices will come back and plateau. If they're high enough, you'll see the occasional recasts mixed in. Much like we see for other in-demand minis like HE Swordmasters, dragon princes, Juan Diaz steeds of slaanesh, etc.
Of course, the speculators might well end up sitting on a load of metal. I see loads of HE and UD warmaster minis sitting on ebay all the time looking for a home. Either they ask for too much and don't sell, or have to unload below retail price. Or they're reduced to shenanigans like making false claims that their minis are discontinued. I suppose now that they are discontinued, the price on widely available stuff like that will go up.
The key unknown is how the other manufacturers will react. If someone like a Eureka jumps in and fills the niches that GW has dominated, then the rare/OOP GW minis will still be premium items. If Warmaster and 10mm (not the same thing, obviously) both die out, then the prices will drop as people give up and sell their collections.
