With so much to take in with the UA-CO merger here's my quick take on their fleet composition...at the end of the day United is going to have a mix fleet of Boeing and Airbus. They'll keep the 787NG and the A320s in their fleet and I expect that all the current narrowbody orders will be kept intact.
I do think however that between the two fleets there will be a change in the widebody orders that are currently on the books.There are still 3 777-200ERs (for CO) as well as the the 787s and A350s:
3 x 777-200ER (CO)
36 x 787-8 (25 UA and 11 CO)
14 x 787-9 (CO)
25 x A350-900 (UA)
I do think that there may be too many widebodies on order here for both carriers combined and thus some part of this total order is going to be cancelled. Given that the 787-8 is going to be the prevalent type (CO/UA will be taking delivery starting next year), I think the A350 order will be cancelled and maybe some 787-8s. I think the new UA will be taking at least 25 787-8 and all the 787-9. They may even opt for more 787-9s.
As far as the narrowbodies are concerned. Look for UA to continue to take delivery of the remainder of the 737/A320 orders but after that the airlines is going to wait and see what both manufacturers turn out in terms of the either the re engined narrowbody or next gen narrowbody. UA might even opt for the C-Series.