That's not his responsibilty at all. Try contributing to an open source project instead of complaining.
1) Your website requires backwards compatibility
2) It's not his problem
Better whine and complain on the internet until someone fixes your problems for you.
It's very easy to handle a Javascript fallback for Slider.js: Instead of having an empty container in which your slider will be templated, put the content for the non-javascript into it.
That's it ;) Just because the Slider Javascript will empty the content of it ;)
(Side thought: maybe I'm wrong, but in 2011, are we still need a JS backwards?)