Should you need to use the fuel from the failed side , you need to apply the fuel imbalance procedure.
By simply opening the X-feed, you might aggravate the fuel imbalance , and end up dry on the live engine side.
Fuel pumps have no clue about « the live side or failed side »
Fuel Pumps do not necessarily have the same delivery pressure , the best pump wins.
For that reason switching off the fuel pumps on the lighter tank is a must as dictated by the fuel imbalance checklist.