With EAGLE it is important to say which version, i.e., pre or post Autodesk. I am only pre-Autodesk but this advice may still apply. Your files should show b## as prior versions. My first attempt would be to go to the preferred grid and try the last backup. If that fails, there may be a group command line you can use, but I am not very good at using the command line.
My last option would be to go to the bastard grid and correct the errors. That is certainly tedious, but is a lit easier than trying to do it using something like the "finest" grid. FYI: Under options, I assigned a function key (F6) to switch between grids. It's very useful. Consider that for the future. In your immediate case, you might assign the preferred grid to the ALT+ grid and the bastard grid to the regular grid while making adjustments.