Both legacy airlines had fairly simple fleets prior to the merger, the combined airline is as complex as UAL was in 2000. Parking the 400's and canceling the 350 will go a fair way in simplifying our fleet. Parking most of the 756 fleet in the coming years and replacing them with 787/321's will finish the process. We will be down to 4 fleet types.
These bumps are just a bump in the road, not a catastrophe. There is as much opportunity created for some, as there is inconvenience for others. Other than GUM, I doubt any pilot will be forced out of a base involuntarily.