Well, assuming hefty doses of handwavium so the astronauts survive the radiation inherent in a wormhole, I believe it would be possible, although it might take some time.
The secret is a total sky galaxy survey, backed up with a corresponding survey from earth such as has been/is being done by HST, Spitzer, and Chandra. Once you findpositively identify four galaxy matches with their red shifts, you can pinpoint the milky way (even if it's hidden behind another galaxy) and determine how much time has elapsed since you left home to transit the wormhole.
I'll let an astronomer do the math for this one.