Hi,
We did the upgrade from 7.3.2 to  8.0.3 that failed and after rollback menu will not appear. I had a look at the log and i find the following messages in the log.

2017-07-27 12:09:30,915 [RD00155D825C0A][Thread:14][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.InvalidOperationException: Could not locate Razor Host Factory type: System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc
at System.Web.WebPages.Razor.WebRazorHostFactory.CreateFactory(String typeName)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at System.Web.WebPages.Razor.WebRazorHostFactory.CreateHostFromConfigCore(RazorWebSectionGroup config, String virtualPath, String physicalPath)
at System.Web.WebPages.Razor.WebRazorHostFactory.CreateHostFromConfig(String virtualPath, String physicalPath)
at System.Web.WebPages.Razor.RazorBuildProvider.GetHostFromConfig()
at System.Web.WebPages.Razor.RazorBuildProvider.CreateHost()
at System.Web.WebPages.Razor.RazorBuildProvider.EnsureGeneratedCode()
at System.Web.WebPages.Razor.RazorBuildProvider.get_CodeCompilerType()
at System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider)
at System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders()
at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath)
at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound)
at System.Web.Compilation.BuildManager.GetCompiledType(VirtualPath virtualPath)
at System.Web.Compilation.BuildManager.GetCompiledType(String virtualPath)
at DotNetNuke.Web.Razor.RazorEngine.CreateWebPageInstance()
at DotNetNuke.Web.Razor.RazorEngine.InitWebpage()
at DotNetNuke.Web.Razor.RazorEngine..ctor(String razorScriptFile, ModuleInstanceContext moduleContext, String localResourceFile)
2017-07-27 12:09:31,006 [RD00155D825C0A][Thread:14][ERROR] DotNetNuke.Services.Exceptions.Exceptions - System.NullReferenceException: Object reference not set to an instance of an object.
at DotNetNuke.Web.Razor.RazorEngine.Render[T](TextWriter writer, T model)

Thanks in advance.

Regards,
Sudeep