Photographs would help, but it may be you need do nothing.
Subwoofers generally have L and R inputs for convenience of connection, but simply sum these two inputs to produce the subwoofer signal.
You should be able to do this externally and send the combined signal to whichever input is undamaged.
Whether this is straightforward or not would depend on where the L/R signals originate and whether they were sent elsewhere as well.
Personally I'd be reluctant to drill it since there is a chance that either the whole pin or drilling swarf could end up in amongst the electronics. This probably would be irrepairable.
Prpbably the least invasive thing to try would be to apply a powerful suction (eg from a workshop vacuum cleaner) to the outside of the socket. You never know - it might work.
Have a look at the construction of the other (intact) plug. If its pin is hollow (they usually are) you might be able to insert (carefully) an epoxy coated cocktail stick down the inside of it.
Nick