I am trying to create a backup plan, and I hope someone can help me out.

Background: Several months ago we booked UA nonstop IAD->DUB for three people on 6/24, returning on 7/5. We need to be in Dublin no later than 11:59pm 6/26 for a scheduled tour, so we have allowed for an extra day just in case. Two weeks ago, UA cancelled our nonstop outbound flight (...in fact, cancelled ALL nonstop IAD->DUB service until 7/1), so we rescheduled to IAD-EWR-DUB, again leaving IAD late afternoon on 6/24, with a several-hour layover in EWR before a 10pm departure which arrives in DUB on 6/25.

The problem: I have noticed that UA has recently been cancelling the IAD-EWR leg with considerable frequency (despite no weather problems in either location), including today (7 days away from our scheduled outbound flight date). I am hoping to create a backup plan, in case they do it to us next Friday.

Having tracked the IAD-EWR flight for a number of days, it appears that when UA cancels this flight, they do so early in the morning on the day of the flight, but by the time they did it today, all WAS-EWR flights were full for the day, and all UA and EI flights WAS-DUB were fully booked for the next several days.

Do we really have no choice at this point but to roll the dice and hope the IAD-EWR flight is not cancelled, or can we create some sort of backup plan?

Thank you in advance for your advice.