Rulings
If Blade Historian leaves the battlefield after first-strike combat damage has been dealt but before regular combat damage (perhaps because it attacked and was destroyed by first-strike combat damage), attacking creatures you control will lose double strike. A creature without double strike won’t deal regular combat damage if it already dealt first-strike damage that turn.
(wotc • 2021-04-16)
Rulings
If Blade Historian leaves the battlefield after first-strike combat damage has been dealt but before regular combat damage (perhaps because it attacked and was destroyed by first-strike combat damage), attacking creatures you control will lose double strike. A creature without double strike won’t deal regular combat damage if it already dealt first-strike damage that turn.
(wotc • 2021-04-16)