I booked using miles the following trip on one award ticket for three people (25000 miles each) including me:

MSP-BZN, BZN-MSP, MSP-LGA-SYR

Assuming the first two legs are finished fine, my question is:

1. what if in the third leg MSP-LGA-SYR, only me show up and take the flight? is there any problem?

2. what if there's weather condition that doesn't permit travel and Delta has to cancel the third leg? Is Delta gonna refund the miles for the entire itinerary? if not, what's the compensation if I refuse their re-arrangement?

3. is Delta's policy different from the other three legacy airlines?

Thanks.