So let’s say Obozo pardons the Clintons. Could the still IRS go after them?
Yes.
Accepting a pardon is an admission of guilt. That’s why no prosecution is needed for a pardon to be issued.
A pardon would not cover the Clinton Foundation, as that would be an admission of its illegality and would open it to endless lawsuits. Probably a pardon for the email scandal only would not have the negative consequences.