Other North & South America Frequent Flyer Programs - Is it OK for only 1 passenger to fly on 2 person ticketed Spirit reservation?

I have a RT flight booked DEN-LAS on Spirit next week. There are 2 passengers on the reservation. My friend can't make the trip so I'm wondering if it's possible for me to fly both outbound and return on this reservation with my travel partner not showing up? I l know I should be able to make the first flight no problem. just wondering if they will void the return portion all together since my travel partner didn't join on the first leg.

I've never flown Spirit, but on any airline one or more of a party can "no show" without voiding the tickets for the other travelers.

Assuming you are not a child, and your "no show" partner is not the accompanying adult. :)