IMO no its not dieing. Many people still use reseller hosting. You cant Over sell ON a VPS and the prices for resellr hosting is cheaper than a VPS and less work for the reseller as the main server owner will need to do things like restoring backups ETC.
Well this is not entirely correct as you can oversell, but you have to have resources to sell in the first place lets say you have a vps with 100 gigs space and 1 tb bandwidth, you can sell plans that all have 20 gigs but until you have used up a grand amount of space. you can still over sell it.