Yes, web sites done in FrontPage will still work. Some of this depends upon
the company that hosts the web site however. For example, if a FrontPage
user has made use items that require the FrontPage Server Extensions and
their web hosting provider decides to stop supporting the FP Server
Extensions, then those parts that relied upon them would not function (such
as the form to email, search componetn, etc). Generally though, I don't
think most hosts will be dumping support for the FP Server extensions for a
number of years to come, especially since tools such as EW and Visual Studio
can use the extensions to publish their webs and projects to a server using
http with the FP Server Extensions.