Of course, we’re assuming Black Widow doesn’t mark Taskmaster’s final appearance, which could always happen as well.
Given that history, and the fact that Black Widow takes place in the past, it’s possible Taskmaster may be working behind the scenes for the good guys in the present day.
I’m hoping that’s not the case, but we’ve lost a fair amount of MCU villains over the years.
It’s possible, though it’d be weird to think he hasn’t been shown to this point.