FWIW, on United, bereavement or medical emergency tickets are treated as 'hardship revenue' and given BP1A. This is the highest level of positive-space boarding priority there is. Right up there with full fare tix. Cannot be downgraded, cannot be denied boarding, CAN get advance seat reservations...

OTOH, using mileage is subject to capacity controls and status for standby... if the cost of a a medical emerg. tix is reasonable, it seems infinitely better to use...last thing you want to worry about at a time of stress is standing by for flights.