Where is the data? is it on the system drive or separate data drive?
Yes slamming off the power would stop the registry from writing back, and stop other minor writes, but if the software used for recovery has a fit about a "dirty" partition/drive it might hinder some things. Doing a chkdsk prior to recovery could write out file data itself.
If it was a virus writing itself to startup from the registry a virus changing or deleting files, mabey it would be a way to save, but probably not for normal delete recovery
Why not just do a quick Undelete without leaving the system? Always have an Undelete tool already installed on the system, saving that write.
Run an undelete tool from a flash drive, or secondary drive/partition if you did not think ahead.
If you are using the write caches of the system, or a disk controller, you could make things worse if a flush of the write data had not yet occured.