Bismarck's operational orders, her rules of engagement as it were, for Operation Rhein, specified that she would be allowed to engage an enemy battleship escorting a convoy in order to give Prinz Eugen a chance to attack the merchant ships with guns and torpedoes. Bismarck was not expected to waste time and ammunition sinking a battleship escort, but to engage in a spoiling action until Prinz Eugen had accomplished her mission. In such a scenario, it is likely that Warspite would engage Bismarck while Exeter attempted to head off the Prinz Eugen. It is unlikely that defence of the convoy would be left to its ASW vessels and might in any event have not been destroyers but corvettes like the Flower-Class. As these had no torpedo armament, and were slow, they posed little threat to the heavy cruiser, so I should imagine that Exeter would have had to face the Prinz Eugen.
Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.