@georgetakei My take on this:
Regardless of what legalities are involved in forcing Pence to testify regarding the insurrection, he remains bound by the oaths he took in Congress and as VP, with the latter reading as:
"I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."
Based on that oath, Pence has both a moral and ethical obligation to do "the best of my [his] ability" with respect to the investigation and prosecution of those who attack this country. That he hasn't done so marks him as someone whose word cannot be trusted and inherent supporter of the attack and attackers.