I have been a classic developer since early 2001 and have now migrated to .net 6 months ago, along with the company I work for.
Now all applications I write (Winforms/Webforms) are all written in C#.
This was obliously not a decision we took lightly and I know Microsoft have mentioned about continual support for classic and the fact that even if they didn't you could still just use the asp.dll from IIS to render all classic pages to the class.
However, do you really think putting off a migration to .NET is a smart move ?
As a employee and a employer I am only looking for .NET developers (Even though we do have some classic applications still running). Also have you tried looking for a classic job lately ? They are pretty much no existent, the ones you do find all mention migrating to .net.
Difference between classic and .net ?
Well as .NET is naturally an OOP language, the first thing I noticed is the power and the re-useablity of all my code. An example of the BIG difference between the two is addons/components.
On a recent project we needed a decent chart program and then we needed to convert the charts to a PDF. In classic you would have to find a decent host who is willing to install these components or buy an expensive dedicated and register it yourself. In .NET we bought the components for both chart and pdf and was sent the dll file for each. All we need to do now is to add the .dll to our project which is as simple as [ Browse > dll file > add to project ] - this now lets me create amazing charts and convert the page to a PDF on the fly - all within a standard shared hosting plan.
I personally think that anyone still coding in classic should really sit down one weekend and plan the migration to .NET as you are already many years behind everyone else and the sooner you migrate the sooner you will see .NET in its full glory.