What happens to Spiegelman's mice as they are forced deeper into "mouse holes"? In what way do they become more "mouse-like"? How might they have responded differently if the Germans had started their program of extermination from the start?

Hmm, interesting. The mice are symbolic of the greater Jewish culture mixed up with a host of stereotypes. The whole "vermin" idea that Hitler had is exploited in the book for ironic effect. Had they been exterminated from the start I don't think the vermin scattering idea would have been as effective.