just my experience

They didn't take my I-94 away since my visa is just checked. For my hu*****and, they took his I-94 away because his visa application was denied (he was a F-1 student with full scholarship). This is different from Canada visa application, where they take away your I-94 even if they are just checking.
On the borader, I didn't have trouble getting back since I have valid I-94. For my hu*****and, we waited in the office of boarder INS for more than one hour and waited on their decision. Finally they let him in with a new I-94. That I-94 has same expiration date but it is written in both Mexicon Language and English.
We got back but the experience has been scary. I don't want to try that again if there is any other choice. The only good thing from that is we got married after we came back from CJ because we realized how important it is to be with each other.
I heard some worse case scenario in the website that I send to your QQH. So if you check there, you will hear a lot of real life story. Then you make the choice.
I said it to keep you informed. It might be better to keep in mind that things could be ugly. Just in case.
Best wishes to you.