The answers to these types of questions will be found in your local PACKAGE RIDER....
Typically, section 12 in most books. Bidding and Delivery Area Openings. Most riders mirror each other.
There are some general rules for situations like this. The most common language that applies is simple.
"when a drivers assigned delivery area is permanently changed by 50% OR MORE of its delivery stops, said driver shall have the right to follow the major portion of the original delivery area. WHEN MORE THAN ONE drivers delivery area is affected, those affected drivers shall be afforded the opportunity amongst themselves to bid the areas affected in accordance with their seniority."
Two points here, if the affected drivers route was eliminated and at least 50% or more was MOVED to another route, that driver SHALL have the right to follow that work regardless of seniority. The word SHALL is the most important word in the sentence.
Secondly, if the affected drivers route was eliminated and the work spread to the other cars in the LOOP, then an immediate re-bid of those affected cars must be made, and starting with loop seniority. Typically, the lowest senior driver will get pushed out of his route.
The important thing to remember is that your package rider contains the language you will need to establish what action to take.
Anytime you see the word SHALL, it doesnt mean maybe, possibly, or could be. Its an affirmative word.
Read your rider.
Peace.