So there's no way of knowing they haven't. I feel like that's a bit above their paygrade (and would they have the time to?). It depends on your paranoia level. If your thoughts flow like a tranquil stream after the first spring day, then copy the data to a new machine and move on with life. If you wonder if the dogs howling in your thoughts are messengers for the prince of darkness, burn everything in a thermite-fueled bonfire.
For me personally, I would destroy the equipment, weep on its grave, and move on. With backups that aren't physically on me. However, most of the data I keep on my machines either lives in the cloud, or is replaceable.
If this work is truly priceless, an audit is in order. First off, take the drive out of the laptop and plug it into an isolated environment -- new computer with no network. A handy-dandy Linux Live CD is great for this. Mount the drive in question, and look through the files -- do you see anything odd? Is anything missing? Any strange windows files? Using Clam AV is also a good choice. Are there any new files you don't recognize? Delete them.
I'd also do the copy over in small pieces while in the Linux Live CD. Unless they're sophisticated enough to put Windows and Linux malware on there, you'd prevent any surveillance programs from autoplaying and finding a new home. I cannot stress this enough -- know what you are copying. Check your project -- Any new additions you don't remember?
After that, use a clean Windows environment and be on the watch for any suspicious activity. Build a good security policy, and next time encrypt your drives! Oh, and toss everything once you've recovered the data. Firmware attacks are real.