Missing first leg of a two leg classic rewards flight — will my itinerary be cancelled?

Hi all,

I have booked a return domestic trip with classic rewards to visit a sick relative this week. Unfortunately it looks like I’m going to have to get there sooner than I originally booked, so I’m looking at purchasing an earlier flight with cash (I don’t have enough points to change my classic rewards flight). I know they have rules about skiplagging etc, I just wanted to know if my entire itinerary will be cancelled if I miss my flight there?

Thanks heaps in advance