I was recently asked whether MSCS/WSFC will become obsolete due to 3rd party HA solutions. I think there will always be a market for 3rd party HA solutions, but many of the enhancements delivered with Windows Server 2008 have reduced the need to explore alternate HA solutions. I think the greater threat to MSCS/WSFC is HA solutions provided by the virtualization vendors, such as Microsoft’s Hyper-V failover clusters (which actually uses WSFC) and VMware HA. These solutions provided by the virtualization platform provide protection in case of host failure, although they currently do not have visibility into the application that is running within the VM.
The real question is what kind of failure do you want to protect against? If physical server failure is your primary concern, then in some cases where MSCS may have previously been deployed, you will see Hyper-V Clusters or VMware HA being deployed instead. In other cases where MSCS/WSFC may have seemed like overkill or was incompatible with the OS or application, you will instead see clustered VMs being deployed because it is easy to install and it supports all applications and operating systems. The mere fact that more workloads will be running per physical server will make it imperative to have some kind of clustering solution so that the failure of a single server does not bring down your entire infrastructure. In many cases, this clustering solution will be provided by the virtualization vendor.
Hyper-V Clusters and VMware HA are easy to implement and have a broad range of support as the protected VM can be running any OS or application. The tradeoff is that you lose the application level monitoring included with MSCS/WSFC. There will always be a class of applications that need application awareness, so MSCS/WSFC or other HA solutions that manage application availability will always be needed to ensure that the application is available, not just the server itself. With that being said, MSCS/WSFC will not become obsolete, but you will see it deployed alongside other cluster solutions provided by the hypervisor vendors..