I can tell you for a fact that more than a few holes in a planes fuselage are not an issue.

Seriously, the bigger issue is in the event a critical item was hit. A hydraulic pump or a line for example.

All these things are taken into consideration during training and evaluations of the actions of the training. (Holes in planes and what not).

Holes the size of standard bullets do nothing more than allow slow pressurization. The masks drop down at a certain point depending on altitude. You put the mask on and your good to go.