I have similar situation coming up with UA (sorry OP for adding on to your thread.)

I have tight connection @ EWR of 50 minutes for a once-a-day international UA flight (domestic connecting to international.) However, there are other *A flights from EWR to the same destination in a couple of hours (albeit with a layover,) Swiss and Turkish. If I miss my flight, do you think UA will put me on Swiss/Turkish? At that point can I pick and choose which airline?

I have flexibility so I don't care if they put me in a hotel for the next day or re-book me on a different airline the same day.