Fireworks CS5 had showcased this feature but had to be pulled in the last moments due to stability issues. Engineers worked on the feature where the png file when crashed, can be recovered and the user will be prompted to recover it the next time Fireworks launches.
On the next launch of Fireworks, it will alert that the files have been recovered. There are cases when the recovered file will need to be re-saved to ensure some smaller things like previews which are not saved when recovering the file.
I remembered one crash where Fireworks CS5 used to crash on editing a symbol which had an empty name. This crash is also fixed along with the other crashes fixed for Fw CS5.1 release.