OP here.

Thanks everyone, I learned a lot about how the airlines work!

While most of your advice is universal, here are few more things about my specific situation that were brought up:
1. We only spent 10,000 miles each for the r/t between ORD and LGA. Good deal! So that takes the $150 redeposit fee option off the table.
2. We each bought our own tickets using our own miles. So we already have separate confirmation numbers.

I'm thinking I'll check the available seats on the plane at the airport kiosk and if there are a decent amount of empty seats, I'll check my wife in and increase the odds for a standby passenger to be seated elsewhere. If the plane is nearly/completely full, I'll leave it alone.