While this could be taken lightly, there is a record of other Google products and services being axed a period of time after something was to stop being deveoped. If you do use this app, you should not have any worries. All of your notes were stored via Google Docs anyways, so you can still retrieve them there if you need to see your notes.
Scratchpad was one of those special apps that came with ChromeOS that worked offline. Any notes that were taken with Scratchpad were synced back to the cloud after you reconnect to the internet.
It isn't the end
Even though Scratchpad could be going away, it isn't he end. There are plenty of other notepad apps for Chrome, and you can even using something live Microsoft Office OneNote Web App if you wish to use a "real" note taking tool that is free to use in the browser. OneNote has sorted tabs and more from just its webapp form.
Right now the app is still on the Chrome Store, so grab it now while you can.