Online Co-op achievement?

[RestlessSpectre]

I don't know if i should have made a new thread or posted this question somewhere else. I apologize in advance just in case.

Anyway, I noticed that one of the achievements was to complete every mission in online co-op mode. My question is (hopefully someone can actually answer this) will you not get this achievement unless you ONLY complete the missions in co-op? I mean.. I know it'll be fun to play co-op, but sometimes I'd like to play offline. However, I don't want to have to go through the game again because I completed a mission offline and it needed to be completed online.

[Zef]

You might have some option to replay missions that you have already completed. Seeing as the game hasn't been released it is difficult to say, so they may have some interesting strategy for co-op achievements.

[Spartan]

It does sometimes suck to play through a game twice if you're looking to get all the achievements, but I think with Crackdown it's going to be a little different. I think that since there are so many ways to go about doing the missions in whatever order you want, and all the fun stuff you can do I can see playing through this game many many times not being a problem.