No way to tell. There's been some estimates how much 90% is still around but hard to verify. You could do a browser search and find some discussions about it. Usually 90% silver dimes, quarters, half dollars, Morgan, Peace are not sent to refiners, few are melted because collectors want to stack them. But there have been times when silver prices spiked up, like in 1980, 2011 where 90% was sold to dealers and sent to refiners for melting, many bags of it.
Currently dealers have been reporting the refiners have enough 90% and sterling silver to refine and don't want to buy it or will only pay lower price. This indicates people are selling at the high prices.
Except for the low mintage years, most well circulated cull Morgan and Peace are worth melt or several dollars over melt.