When a prefix which was having 2 equal path next hop(ECMP) got a route withdraw from one nexthop, prefix should point to a group with only one nexthop which is not happening today. 

Suppose we get prefix X from DC-GW A and DC-GW B, now X will point to a select group with A and B as buckets. But now when DC-GW B withdraws X, X should point to a group with only A