Pence may wish to come clean if he ever actually had any meetings with Russians, or if he knows anyone who did — and what these meetings were for. Before he’s put under oath and he has to either tell the truth or commit perjury.
Because ducking and dodging will only cause the glare of the spotlight to shine more brightly on him, and I doubt he wants that. If he’s got anything to hide, it will be found out. It’s just a matter of when.