You can't generalize this to all guys, everyone is different. I doubt any guy would ever get MAD at their girlfriend unless they're an idiot and a jerk. I mean the guy had an equal part in it too. I think the only reason a guy would ever get mad would be if a girl got pregnant on purpose (like the girl said she was on the pill but really wasn't) cause that's intentional deceit. Otherwise, getting mad at her is stupid.
If the girl decided to keep the child I think a fair number of guys would probably want to leave her (again, depends on the seriousness of the relationship) simply because they're not ready for children. Those are what we call dead beat dads. On the other hand, if it's a more committed longer relationship then the reaction would probably be one of shock, and of course anxiety. I mean it's a huge lifestyle change, but then with a longer committed relationship there's a greater likelihood that the guy will be scared but wouldn't just leave the girl.
I mean. this happened to me once so I can speak personally about it. We found out my girlfriend was pregnant and when she told me, I at first had a mini-panic attack thinking, "oh my god, what are my parents gonna say? are we going to have to drop out of college? I'm not ready for this. holy shit!" (etc. etc.) but after the initial shock wore off I realized she was going through the same thing if not worse. I still wanted to be with her and wasn't about to leave over this so I talked it over with her for a period of a couple of weeks. I'll admit, in my fear I kind of tried to persuade her to get the abortion and she did. I still think it was the right choice, we weren't ready for that, but I feel like an ass now for suggesting it to her and indicating that I would prefer it.
As for the last part of your question, no we weren't scared about me getting her pregnant again afterwards, so that wasn't an issue. Well we were a little, but it just means we were a little more cautious, not too scared to stop having sex.
So in summation, it's different for each guy, varies by age and maturity level and level of responsibility. All will probably have the initial reaction of fear and anxiety, but as to whether or not they want to stick it out and support their girlfriend, or bail out and get away. that's a matter of the guy's personality.