Yes, the 'Restore Previous Index' option allows you to revert / restore the data files of your index to the state in which they existed prior to your most recent index attempt / completion, either via a Scheduled or Index on Demand request.

In this manner, if a Scheduled or Index on Demand request fails for any reason, or if a error was made on a page or pages, and you do not wish to wait for another index request to complete for correcting the problem, you may immediately revert to your last index by executing this option.

To restore your previous index, login to your account, click on the 'Spider' tab, and under the 'Index Options' section, select the 'Restore Index' link.

Note:  If you are experiencing problems with your current index, be sure to select the 'Restore Previous Index' button BEFORE requesting another spider. If another spider has been requested, both your current and previous indexes may become invalid.