This is a Third Conditional sentence where the if-clause is in the Past Perfect tense (had been). Therefore, the main clause must contain would have + past participle (come).

১. Would come is used in Second Conditional sentences with past simple.
২. May have come indicates a possibility in the past but lacks conditional logic.
৩. May come is used for present or future possibilities in real conditions.

অতিরিক্ত তথ্য: Conditional sentences are essential for expressing hypothetical situations in English.