So much ado by the Valeyard and the Master over the Doctor's death makes the Doctor wary of being made decoy for some other, truer target. Continuing in the Matrix itself, he may find both them and the answers he seeks.
Did You Know?
had no idea that Peri's death had been undone until much later. According to Colin Baker
on the 2008 DVD commentary, this conceit was the result of him idly asking a production team member if Peri had "really" died in Mindwarp, coupled with negative audience reaction to the character's apparent death. See more
I really must curb these urges. I've no wish to be contaminated by your whims and idiosyncrasies.