My sister wants to marry a nice Mexican man?

She's really not into religion (but still believes in Jesus). I spoke with her last night and she sounds very happy. I've met the dude before and he's actually a great guy so I didn't kick his *** like I was originally going to do (ohhh the protectiveness of big brothers). But she says she will not convert to Catholicism just to please his mother. I'm proud of her (I am an atheist and bow to no religion) but feeling a bit iffy about the outcome of this because he is very religious and I don't want her to have her heart broken in the future. Curious, what are different things that could happen?