Killing of Shrink data file command will cause rollback and it will take more time to rollback depending upon the data file size. Sometime rollback will not happen for a days for larger files and if you recycle SQL server, database may go in recovery forever.

If you want to shrink data file, do it in smaller chuck of size from large free space available and continue. Do not shrink multiple data files from the same database as it may go in deadlock situation where recovery of database is a problem.

You should shrink one data file at a time from the database to avoid deadlocks and recovery issues.