if the worst comes to the worst idiom UK (US if worse/worst comes to worst)
如果最坏的事情发生；如果发生最糟的情况
if the situation develops in the most serious or unpleasant way
We should be in when you arrive, but if the worst comes to the worst, the neighbours have a spare key and will let you into the house. 你到的时候我们应该在家，万一不在，邻居家还有一把备用钥匙，能让你进屋。