upgrade overwrite

I have a problem where for some reason a couple of my sites are suddenly appearing with the upgrade files installed in the domains route directory asking for ther information to continue the upgrade. I know from a previous attempt that if I start it corrupts the data base. The person whose owns the blog has not backed up. Any ideas how I can get their blog back without losing all the posts to date. They are running 2.3.1 and the upgrade files are for 2.3.3