A while ago I had set up a flight KMLI-KORD… On Expert. Usually it’s about 40 minutes total. I had gotten up to cruise altitude, was fully LNAV with about 30 minutes to TOD.
Household plans changed, I put my phone in my pocket, and it was about an hour later that I switched back to IF. My flight was about 28 minutes to TOD… Proceeded to finish the flight completely normally.
Everything I’ve read says that the plane will continue along the flight path until I return or it runs out of fuel.