Let's start here with The Washington Post:
Pence’s decision to drop the appeal means he will probably testify under oath about Trump’s attempts to pressure him, and he could be a key witness.
The NYTimes has a little more:
From shortly after the election until Jan. 6, Mr. Pence was subjected to an intense pressure campaign from a range of Mr. Trump’s associates outside the government, including John Eastman, a lawyer working with the president, and from Mr. Trump himself. Mr. Pence had his advisers research what his powers were with regard to Jan. 6. Over time, he made clear to Mr. Trump that he did not believe he had the authority that the president insisted he did to unilaterally overturn the results of the Electoral College vote.
By Jan. 5, Mr. Trump’s pressure campaign had become so heated that Mr. Short, who was then Mr. Pence’s chief of staff, called the vice president’s lead Secret Service agent to his West Wing office to tell him that Mr. Trump was going to turn on Mr. Pence, and that they might have a security risk.
Hmm. Trump's pressure campaign on January 5th, huh?
What else happened the day before Trump's mob stormed The Capitol?
This from CNN:
The committee also released call logs from the days leading up to January 6, 2021 painting a fuller picture of who the former president was speaking to as he and his allies were plotting for him to stay in office, the first time the panel is releasing White House call logs in their entirety.
The logs have been crucial to the panel’s investigation in piecing together a timeline of events. While the log for January 6 has a seven-hour gap, the committee has gone to great lengths to fill in that part of the timeline through witness interviews and other records.
The day before the US Capitol attack, Trump spoke to then-Vice President Mike Pence. After that conversation, Trump spoke with Pennsylvania state Sen. Doug Mastriano, who helped fuel Trump’s election lies in the state, and then the switchboard operator left a note “that Senator Douglas Mastriano will be calling in for the Vice President.” [Emphasis added.]
You can see the call log here. You can see the messages involving Pennsylvania State Senator Doug Mastriano are here:
I imagine it's would be a pretty good bet that Pennsylvania State Senator Doug Mastriano was part of Trump's "intense pressure campaign" to get the then-VP Pence to delay the electoral count to keep Trump in power.
Will Doug's name come up in Pence's testimony?
Will anyone please ask Doug himself what he knows about Trump's pressure campaign?
Because he was certainly an active part of it.