Sorry to hear about the issue with the data mart. You are correct that you will need to re-import the companies from the legacy integration page. Doing this will import the companies with a -Curr at the end of the names.
In order to get the existing reports to run with the legacy provider, you will need to update the Company references in the Report Definitions and Trees to use the -Curr version of the company. If you only have a few reports, this is a pretty fast process. If you have a lot of report, you may want to log a support case to explore other options.