If you've ever had a computer, external hard-drive, and/or smart phone "crash", then you know it's one of the words feelings in the world. Like any grieving process, first comes denial, anger, bargaining, depression, and finally, acceptance. I write this with a bit humor - although - if the device contains your client's files, then it could certainly be something that will make or break your business.
It goes without saying that you should always back up your work at least on three different devices and one of them could be in the form of a cloud. In the even that you find yourself in the unfortunate situation where your device has crashed - either due to a mechanical error, it got wet, it was dropped - and you do not have a back up of these precious files, you may want to look into data recovery. I would personally recommend Drive Savers.
Be forewarned: their services are very expensive. The good news is that they have an educational partnership to sign up for; click "here" for details. Evaluations are free; you only pay if your data is recovered; free shipping is included! If you're willing to wait, you may want to opt for the "Economy" option, which is more cost effective. You could have results in 5-7 business days.
"Data Recovery by DriveSavers." Data Recovery by DriveSavers. N.p., n.d. Web. 08 Dec. 2016.