Better than falling back to #!hashbang / document fragment navigation - situation allowing - is falling back to a full web page load. (There is even tech allowing for graceful fallback to full form submissions in lieu of AJAX'd form submissions.)
Only ancient browsers fail to support the HTML5 History API. Currently, that is around 10% of the web. Your customers are likely to have a newer browser than IE 9 if they have a budget for technology at all.
★ The problem with embracing the hash for navigation is that you are now committed to running JS on your root FOREVER to detect those URLs - or old bookmarks & links & social media posts will break ★
